研究者詳細 - 加藤　珠樹

論文 - 加藤　珠樹

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Squaraine-Peptide Conjugates as Efficient Reporters of Neutrophil Extracellular Traps-Mediated Chronic Inflammation 査読有り国際誌

Mavileti S.K., Bila G., Utka V., Bilyy R., Bila E., Butoi E., Gupta S., Balyan P., Kato T., Pandey S.S.

ACS Applied Materials and Interfaces 17 ( 6 ) 9140 - 9154 2025年02月

記述言語：英語掲載種別：研究論文（学術雑誌）

The excessive and uncontrolled release of neutrophil extracellular traps (NETs) is increasingly linked to the pathogenesis of various inflammatory diseases, cardiovascular disorders, and cancers. Real-time, non-invasive detection of NETs is crucial for understanding their role in disease progression and developing targeted therapies. Current NETs detection methods often lack the necessary specificity and resolution, particularly in vivo and ex vivo settings. To address this, we have developed novel near-infrared squaraine-peptide conjugates by rational molecular design as reporters of NETosis by targeting the protease activity of neutrophil elastase (NE). These self-quenching, cell-impermeable probes enable the precise real-time detection and imaging of NETs. The Förster resonance energy transfer (FRET)-based probe, Hetero-APA, demonstrated high specificity in detecting NETs in vitro and in vivo, generating strong fluorescence in NETs-rich environments. To overcome the limitations of FRET-based probes for ex vivo imaging, we designed SQ-215-NETP, a non-FRET-based probe that covalently binds to the NE. SQ-215-NETP achieved an unprecedented imaging resolution of 90 nm/pixel in human coronary thrombi, marking the first report of such high resolution with a low molecular weight probe. Additionally, SQ-215-NETP effectively detected NETs by flow cytometry. These results highlight the potential of these probes in NETosis detection, offering promising tools for enhanced diagnostics and therapeutic strategies in managing NET-mediated inflammatory diseases and cancers.

DOI： 10.1021/acsami.4c20658

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NIR-Sensitive Squaraine Dye—Peptide Conjugate for Trypsin Fluorogenic Detection 査読有り国際誌

Balyan P., Gupta S., Mavileti S.K., Pandey S.S., Kato T.

Biosensors 14 ( 10 ) 2024年10月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Trypsin enzyme has gained recognition as a potential biomarker in several tumors, such as colorectal, gastric, and pancreatic cancer, highlighting its importance in disease diagnosis. In response to the demand for rapid, cost-effective, and real-time detection methods, we present an innovative strategy utilizing the design and synthesis of NIR-sensitive dye–peptide conjugate (SQ-3 PC) for the sensitive and selective monitoring of trypsin activity by fluorescence ON/OFF sensing. The current research deals with the design and synthesis of three unsymmetrical squaraine dyes SQ-1, SQ-2, and SQ-3 along with a dye–peptide conjugate SQ-3-PC as a trypsin-specific probe followed by their photophysical characterizations. The absorption spectral investigation conducted on both the dye alone and its corresponding dye–peptide conjugates in water, utilizing SQ-3 and SQ-3 PC respectively, reveals enhanced dye aggregation and pronounced fluorescence quenching compared to observations in DMSO solution. The absorption spectral investigation conducted on dye only and corresponding dye–peptide conjugates in water utilizing SQ-3 and SQ-3 PC, respectively, reveals not only the enhanced dye aggregation but also pronounced fluorescence quenching compared to that observed in the DMSO solution. The trypsin-specific probe SQ-3 PC demonstrated a fluorescence quenching efficiency of 61.8% in water attributed to the combined effect of aggregation-induced quenching (AIQ) and fluorescence resonance energy transfer (FRET). FRET was found to be dominant over AIQ. The trypsin-mediated hydrolysis of SQ-3 PC led to a rapid and efficient recovery of quenched fluorescence (5-fold increase in 30 min). Concentration-dependent changes in the fluorescence at the emission maximum of the dyes reveal that SQ-3 PC works as a trypsin enzyme-specific fluorescence biosensor with linearity up to 30 nM along with the limit of detection and limit of quantification of 1.07 nM and 3.25 nM, respectively.

DOI： 10.3390/bios14100458

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Clarifying the role of carboxyl functionality in squaraines towards aggregation and self-assembly through photophysical characterization and BSA interactions 査読有り国際誌

Mavileti S.K., Kato T., Pandey S.S.

Journal of Molecular Structure 1309 2024年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

The demand for near-infrared (NIR) probes with robust and stable fluorescence signals has surged, driven by their applications in optical sensing and bioimaging. Squraine dyes as NIR fluorescent probes have gained significant traction. However, understanding their behavior in aqueous media is important for their successful application. Herein we report the synthesis and photophysical characterization of carboxy-functionalized unsymmetrical squaraine dyes capable of light absorption and emission in the near-infrared (NIR) wavelength region. Structural variations in alkyl chain length, and spacer chain length between the primary chromophore and –COOH group were systematically introduced to investigate their impact on self-assembly in aqueous media leading to dye aggregation and their differential interactions with Bovine Serum Albumin (BSA) as a model protein. In phosphate buffer (PB) the absorption intensity decreased drastically along with pronounced shoulders due to dye aggregation leading to complete fluorescence quenching. However, in the presence of BSA, the intensity of shoulder bands reduced coupled with a sharp increase in the absorption associated with monomeric dye with the increasing concentration of BSA, indicating the prevention of dye aggregation owing to dye-BSA interactions. The prevention of dye aggregation due to dye-BSA interaction also led to a tremendous increase in the fluorescence intensities as a function of the increasing BSA concentrations. Site-selective study off BSA showed that these dyes bind preferably at Site-II using hydrophilic interactions. Thus, these dyes show great potential as FRET or fluorescent on/off probes for biosensing, non-covalent labeling of proteins, and fluorescent probes for bioimaging.

DOI： 10.1016/j.molstruc.2024.138226

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A biocompatible NIR squaraine dye and dye-antibody conjugates for versatile long-term in vivo fluorescence bioimaging 査読有り国際誌

Priyanka N., Bila G., Mavileti S.K., Bila E., Negrych N., Gupta S., Tang L., Bilyy R., Pandey S.S., Kato T.

Materials Advances 5 ( 9 ) 3940 - 3949 2024年03月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The demand for dependable near-infrared (NIR) probes, capable of sustained fluorescence within living systems and facile conjugation with biomolecules like antibodies and proteins, has been significantly on the rise, attributed to the substantial rise in the use of NIR imaging techniques and devices, with extensive integration into clinical diagnostics. Antibody conjugates are vital for targeted and selective bioimaging, enabling precise visualization of specific biomolecules within complex biological systems. Their multiplexing capability allows simultaneous detection of multiple targets, while their dynamic imaging capability enables real-time monitoring of cellular processes. Clinically, antibody conjugates have significant applications in disease prognosis, diagnosis, and monitoring. In this work, we report the synthesis of a new symmetrical NIR squaraine dye (SQ-58) with multiple carboxy anchoring groups for ease of coupling with antibodies. The dye showed decreased absorption and fluorescence intensity in phosphate buffer (PB) due to enhanced dye-aggregate formation. However, in the presence of bovine serum albumin (BSA) in PB, SQ-58 showed an enhanced fluorescence signal along concentrations of BSA. SQ-58 showed no cytotoxicity when tested in white laboratory mice while providing strong fluorescence when injected in vivo. Conjugation of SQ-58 through the carboxylic groups to the isotypic mouse IgG antibodies (IgG-SQ-58) resulted in uniform distribution of the targeted molecule in the whole cardiovascular system. The NIR signal of IgG-SQ-58 was stable for at least 7 days allowing the possibility of long-term imaging. Conjugation of SQ-58 to antibodies raised against NK-Ly lymphoma tumor cells allowed efficient discrimination of tumor cells grown in the abdomen of laboratory mice. Thus, to the best of our knowledge, we report for the first time a biocompatible NIR dye, SQ-58, that can be easily conjugatable to biomolecules, and its antibody conjugates for a wide range of bioimaging applications.

DOI： 10.1039/d4ma00212a

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Design and Synthesis of Novel Squaraine-Based Fluorescent Probe for Far-Red Detection of Chymotrypsin Enzyme 査読有り国際誌

Gupta S., Priyanka , Mavileti S.K., Pandey S.S., Kato T.

Molecules 29 ( 6 ) 2024年03月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Chymotrypsin, a crucial enzyme in human digestion, catalyzes the breakdown of milk proteins, underscoring its significance in both health diagnostics and dairy quality assurance. Addressing the critical need for rapid, cost-effective detection methods, we introduce a groundbreaking approach utilizing far-red technology and HOMO-Förster resonance energy transfer (FRET). Our novel probe, SQ-122 PC, features a unique molecular design that includes a squaraine dye (SQ), a peptide linker, and SQ moieties synthesized through solid-phase peptide synthesis. Demonstrating a remarkable quenching efficiency of 93.75% in a tailored H2O:DMSO (7:3) solvent system, our probe exhibits absorption and emission properties within the far-red spectrum, with an unprecedented detection limit of 0.130 nM. Importantly, our method offers unparalleled selectivity towards chymotrypsin, ensuring robust and accurate enzyme detection. This pioneering work underscores the immense potential of far-red-based homo-FRET systems in enabling the sensitive and specific detection of chymotrypsin enzyme activity. By bridging the gap between cutting-edge technology and biomedical diagnostics, our findings herald a new era of enzyme sensing, promising transformative advancements in disease diagnosis and dairy quality control.

DOI： 10.3390/molecules29061282

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Photophysical Characterization and Biointeractions of NIR Squaraine Dyes for in Vitro and in Vivo Bioimaging 査読有り

Mavileti S.K., Bila G., Utka V., Bila E., Kato T., Bilyy R., Pandey S.S.

ACS Applied Bio Materials 7 ( 1 ) 416 - 428 2024年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

The increasing demand for reliable near-infrared (NIR) probes exhibiting enduring fluorescence in living systems and facile compatibility with biomolecules such as peptides, antibodies or proteins is driven by the increasing use of NIR imaging in clinical diagnostics. To address this demand, a series of carboxy-functionalized unsymmetrical squaraine dyes (SQ-27, SQ-212, and SQ-215) along with non-carboxy-functionalized SQ-218 absorbing and emitting in the NIR wavelength range were designed and synthesized followed by photophysical characterization. This study focused on the impact of structural variations in the alkyl chain length, carboxy functionality positioning, and spacer chain length on dye aggregation and interaction with bovine serum albumin (BSA) as a model protein. In phosphate buffer (PB), the absorption intensity of the dyes markedly decreased accompanied by pronounced shoulders indicative of dye aggregation, and complete fluorescence quenching was seen in contrast to organic solvents. However, in the presence of BSA in PB, there was a enhancement in absorption intensity while regaining the fluorescence coupled with a remarkable increase in the intensity with increasing BSA concentrations, signifying the impact of dye-BSA interactions on preventing aggregation. Further analysis of Job’s plot unveiled a 2:1 interaction ratio between BSA and all dyes, while the binding studies revealed a robust binding affinity (Ka) in the order of 107/mol. SQ-212 and SQ-215 were further tested for their in vitro and in vivo imaging capabilities. Notably, SQ-212 demonstrated nonpermeability to cells, while SQ-215 exhibited easy penetration and prominent cytoplasmic localization in in vitro studies. Injection of the dyes into laboratory mice showcased their efficacy in visualization, displaying stable and intense fluorescence in tissues without toxicity, organ damage, or behavioral changes. Thus, SQ-212 and SQ-215 are promising candidates for imaging applications, holding potential for noninvasive cellular and diagnostic imaging as well as biomarker detection when coupled with specific vectors in living systems.

DOI： 10.1021/acsabm.3c00997

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Prediction and Validation of Proline-containing Tripeptides with Angiotensin I-converting Enzyme Inhibitory Activity Using Machine Learning Models 査読有り国際誌

Hatakenaka T., Fujimoto Y., Okamoto K., Kato T.

Letters in Drug Design and Discovery 21 ( 15 ) 3069 - 3075 2024年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：記事・総説・解説・論説等（その他）

Background: Numerous inhibitory peptides against angiotensin I-converting enzyme, a target for hypertension treatment, have been found in previous studies. Recently, machine learning screening has been employed to predict unidentified inhibitory peptides using a database of known inhibitory peptides and descriptor data from docking simulations. Objective: The aim of this study is to focus on angiotensin I-converting enzyme inhibitory tripeptides containing proline, to predict novel inhibitory peptides using the machine learning algorithm PyCaret based on their IC50 and descriptors from docking simulations, and to validate the screening method by machine learning by comparing the results with in vitro inhibitory activity studies. Methods: IC50 of known inhibitory peptides were collected from an online database, and descriptor data were summarized by docking simulations. Candidate inhibitory peptides were predicted from these data using the PyCaret. Candidate tripeptides were synthesized by solid-phase synthesis and their inhibitory activity was measured in vitro. Results: Seven novel tripeptides were found from the peptides predicted to have high inhibitory activity by machine learning, and these peptides were synthesized and evaluated for inhibitory activity in vitro. As a result, the proline-containing tripeptide MPA showed high inhibitory activity, with an IC50 value of 8.6 µM. Conclusion: In this study, we identified a proline-containing tripeptide with high ACE inhibitory activity among the candidates predicted by machine learning. This finding indicates that the method of predicting by machine learning is promising for future inhibitory peptide screening efforts.

DOI： 10.2174/0115701808274195231113053944

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Substrates incorporating unnatural amino acids are separately detectable for chymotrypsin and subtilisin with similar specificity 査読有り

Yamawaki Y., Kato T.

Results in Chemistry 6 2023年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Protease specificity depends on the three-dimensional structure and sequence of the protease, and each protease plays a different role. Chymotrypsin and subtilisin have similar specificity for recognizing aromatic and hydrophobic amino acid residues. Previous methods using natural amino acids have difficulty in separately detecting proteases with similar specificity. To overcome this, we developed an effective substrate incorporating unnatural amino acids using a simple method that changes only one residue of a substrate. Various 7-amino-4-methylcoumarin (AMC) peptide substrates were synthesized in terms of hydrophobicity, aromaticity, and conformation, including unnatural amino acids 2-amino-4-ethylhexanoic acid (AEH) and cyclohexylalanine (Cha). Although AEH substrate is highly hydrophobic, steric hindrance based on the branched side chain of AEH residue reduced the recognition of the substrate by the two proteases. Cha substrate with a six-membered ring side chain was most preferably recognized by chymotrypsin but was slightly recognized by subtilisin. This shows that Cha substrate can separately detect the two proteases with similar specificity. Therefore, these results indicate that protease with similar specificities is separately detectable by substrates with a side chain having structural degrees of freedom that provide different steric hindrance.

DOI： 10.1016/j.rechem.2023.101217

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In Vitro and In Silico Studies on Angiotensin I-Converting Enzyme Inhibitory Peptides Found in Hydrophobic Domains of Porcine Elastin 査読有り国際誌

Toshiya Hatakenaka,Tamaki Kato, Kouji Okamoto

Molecules 28 ( 8 ) 3337 2023年04月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

One of the most striking aspects of the primary structure in the hydrophobic domains of the tropoelastin molecule is the occurrence of the VAPGVG repeating sequence. Since the N-terminal tripeptide VAP of VAPGVG showed a potent ACE inhibitory activity, the ACE inhibitory activity of various derivatives of VAP was examined in vitro. The results showed that VAP derivative peptides VLP, VGP, VSP, GAP, LSP, and TRP exhibited potent ACE inhibitory activities, while the non-derivative peptide APG showed only weak activity. In in silico studies, the docking score S value showed that VAP derivative peptides VLP, VGP, VSP, LSP, and TRP had stronger docking interactions than APG. Molecular docking in the ACE active pocket showed that TRP, the most potent ACE inhibitory peptide among the VAP derivatives, had a larger number of interactions with ACE residues in comparison with APG and that the TRP molecule appeared to spread widely in the ACE pocket, while the APG molecule appeared to spread closely. Differences in molecular spread may be a reason why TRP exhibits more potent ACE inhibitory activity than APG. The results suggest that the number and strength of interactions between the peptide and ACE are important for the ACE- inhibitory potency of the peptide.

DOI： 10.3390/molecules28083337

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Novel cyclic undecapeptides immobilized on reduced graphene oxide surface for enhanced antibacterial properties 査読有り

Farrag H.N., Zheng A.L.T., Sabidi S., Wu Y., Ikeno S., Maeda T., Andou Y., Kato T.

International Journal of Environmental Science and Technology 21 ( 2 ) 1481 - 1492 2023年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The incorporation of antimicrobial peptides (AMPs) in graphene-based materials is a growing strategy to overcome the shortcomings presented by conventional antimicrobial nanomaterials derived from metal/metal oxide. In this study, novel cyclic undecapeptides CH1 and CW2 (KRQRFYFRQRK and QNKRFYFRKNQ, respectively) were successfully synthesized. The cyclic peptides were then immobilized on the reduced graphene oxide (rGO) surface using a water-soluble carbodiimide (EDCI/HCl) linker. The structural, morphology, and chemical characterizations of the antimicrobial graphene material were carried out using SEM, Raman, FTIR, XRD, and XPS. From our result, the peptide/rGO composite showed an improved antibacterial effect towards gram-positive (Staphylococcus aureus) and gram-negative (Pseudomonas aeruginosa). The enhanced antibacterial property is attributed to the synergistic effect of the sharp edges of rGO and the amphipathic moieties of the cyclic peptides.

DOI： 10.1007/s13762-023-05035-z

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Design and Synthesis of Novel Squaraine Dye with Highly Enhanced Far-Red Fluorescence and its Interaction with a Model Protein 査読有り

Gupta S., Yamawaki Y., Pradhan S., Pandey S.S., Kato T.

Physica Status Solidi (A) Applications and Materials Science 220 ( 24 ) 2023年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Novel amine-functionalized symmetrical squaraine (SQ)-dye and fluorescein isothiocyanate (FITC)–SQ–FITC dye conjugate are designed and successfully synthesized, followed by their structural and photophysical characterizations. Symmetrical SQ dye exhibits complete fluorescence quenching in polar solvents, which is explained by considering photoinduced electron transfer (PET) as a dominant quenching pathway. In contrast, FITC–SQ–FITC dye conjugate results in a decrease in an aggregation of both SQ and FITC units and about 47 times enhancement in the far-red fluorescence appearing at 674 nm. This profound enhancement in the far-red fluorescence is explained by the synergistic influence of suppression of aggregation-induced quenching (ACQ) and PET. This newly designed FITC–SQ–FITC dye conjugate shows complete quenching of the far-red fluorescence in phosphate buffer saline (PBS) owing to very strong dye aggregation, as confirmed by spectral absorption investigation. In PBS, it strongly interacts with bovine serum albumin (BSA) (Ka = 1.1 × 104 m−1) used as a model protein breaking the dye aggregation by BSA and increasing far-red fluorescence associated with SQ as a function of increasing BSA concentration. A profound 117 times increase in fluorescence at 674 nm with 25 times of BSA concentration suggests that the designed FITC–SQ–FITC is an excellent far-red probe for dye-protein interaction.

DOI： 10.1002/pssa.202300226

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Design, Synthesis, and Photo-Responsive Properties of a Collagen Model Peptide Bearing an Azobenzene 査読有り

Daisuke Sato, Hitomi Goto,Yui Ishizaki,Tetsuya Narimatsu, Tamaki Kato

Organics 3 ( 4 ) 415 - 429 2022年10月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Collagen is a vital component of the extracellular matrix in animals. Collagen forms a characteristic triple helical structure and plays a key role in supporting connective tissues and cell adhesion. The ability to control the collagen triple helix structure is useful for medical and conformational studies because the physicochemical properties of the collagen rely on its conformation. Although some photo-controllable collagen model peptides (CMPs) have been reported, satisfactory photo-control has not yet been achieved. To achieve this objective, detailed investigation of the isomerization behavior of the azobenzene moiety in CMPs is required. Herein, two CMPs were attached via an azobenzene linker to control collagen triple helix formation by light irradiation. Azo-(PPG)10 with two (Pro-Pro-Gly)10 CMPs linked via a photo-responsive azobenzene moiety was designed and synthesized. Conformational changes were evaluated by circular dichroism and the cis-to-trans isomerization rate calculated from the absorption of the azobenzene moiety indicated that the collagen triple helix structure was partially disrupted by isomerization of the internal azobenzene.

DOI： 10.3390/org3040027

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Accessing the anti-microbial activity of cyclic peptide immobilized on reduced graphene oxide 査読有り

Zheng A.L.T., Farrag H.N., Sabidi S., Kato T., Maeda T., Andou Y.

Materials Letters 304 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

Herein, we prepared and characterized two antimicrobial cyclic peptides immobilized on reduced graphene oxide (rGO) and accessed their anti-bacterial towards Gram-negative (Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacterias. The covalent interaction between the tyrosine and histidine based cyclic peptides and the rGO occurred via the carboxylic groups of the reduced graphene and the amino side chain groups of the cyclic peptides. A selective antibacterial effect is observed for the cyclic peptides functionalized rGO. The inhibition zone test showed that both the tyrosine and histidine cyclic based peptide immobilized on rGO exhibited higher anti-bacterial potency towards the bacteria in comparison to bare rGO which can be attributed to the synergistic effect of the antimicrobial peptide and rGO.

DOI： 10.1016/j.matlet.2021.130621

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Design and synthesis of novel peptides to protect ferulic acid against ultraviolet radiation based on domain site iia of bovine serum albumin 査読有り

Wu Y., Farrag H.N., Kato T., Li H., Ikeno S.

Biomolecules 11 ( 9 ) 2021年09月

記述言語：英語掲載種別：研究論文（学術雑誌）

Ferulic acid (FA) is known for its excellent antioxidant properties, which can provide many health benefits. One of its drawbacks is its instability under UVA light, which limits its potency. In this study, the new peptides LW2 (QNKRFYFRKNQ) and CW2 (a cyclic form of LW2) were designed based on bovine serum albumin site IIA conformation. A UVA irradiation experiment was performed to investigate the protective ability of these peptides towards FA against UVA damage. The percentages of FA remaining under UV irradiation due to the protection of CW2 and LW2 were 83% and 76%, respectively. The results showed the importance of the cationic residues and hydrophobic residues included in the peptide sequences. Moreover, the cyclic rigid structure showed greater protective ability as compared to its linear counterpart.

DOI： 10.3390/biom11091285

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Design, synthesis and antibacterial studies of novel cationic amphipathic cyclic undecapeptides and their linear counterparts against virulent bacterial strains 査読有り

Farrag H.N., Maeda T., Kato T.

Scientia Pharmaceutica 89 ( 1 ) 1 - 11 2021年03月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Bacteria have acquired resistance against almost all antibiotics because of the misuse of antibacterial agents and long periods of treatment. Antimicrobial peptides (AMPs) are one of the most encouraging candidates to solve this problem, as they possess high prokaryotic selectivity, and affect the bacteria by a unique mode of action. Novel cyclic undecapeptides (QNRNFYFNRNQ and QNRNFHFNRNQ) and their linear counterparts were investigated for their antibacterial activity against virulent strains. The minimal inhibitory concentration (MIC) values showed that tyrosine and histidine AMPs have promising antibacterial activity against virulent bacteria. The MIC values against the P. aeruginosa PA14, E. coli O157:H7 CR3, S. aureus 209P, and B. subtilis ATCC 6633 bacterial strains were evaluated for the cyclic peptide containing tyrosine, and their values were 6.25, 12.5, 12.5, and 12.5 µM, respectively. Meanwhile, for the linear form, they were 9.3, 12.5, 12.5, and 12.5 µM, respectively. The cyclic-peptide–containing histidines’ MIC values were 6.25, 3.1, 6.25, and 3.1 µM, respectively. Meanwhile, for the linear form, they were 3.1, 3.1, 3.1, and 6.25 µM, respectively. The antibacterial activities of the new AMPs were compared with that of gentamicin sulfate, and showed relatively higher potencies. Time-inhibition studies demonstrated the rapid antibacterial effects of the novel AMPs, which were more likely to be concentration-dependent, rather than time-dependent. At double the MIC concentration, all of the tested peptides exhibited relatively stable antibacterial effects up to 24 h, especially the peptides containing tyrosine, which showed an improved antibacterial effect.

DOI： 10.3390/scipharm89010010

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The effect of a peptide substrate containing an unnatural branched amino acid on chymotrypsin activity 査読有り

Yamawaki Y., Yufu T., Kato T.

Processes 9 ( 2 ) 1 - 8 2021年02月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

7-Amino-4-methylcoumarin (AMC) is a low molecular weight fluorescent probe that can be attached to a peptide to enable the detection of specific proteases, such as chymotrypsin, expressed in certain diseases. Because this detection depends on the specificity of the protease toward the peptidyl AMC, the development of specific substrates is required. To investigate the specificity of chymotrypsin, peptidyl AMC compounds incorporating four different amino acid residues were prepared by liquid-phase synthesis. Two unnatural amino acids, 2-amino-4-ethylhexanoic acid (AEH) and cyclohexylalanine (Cha), were used to investigate the substrate specificity as these amino acids have structures different from natural amino acids. AEH was synthesized using diethyl acetamidemalonate as a starting material. The substrate containing Cha had high hydrophobicity and showed a high reaction velocity with chymotrypsin. Although the AEH substrate with a branched side chain had high hydrophobicity, it showed a low reaction velocity. The substrate containing the aromatic amino acid phenylalanine was less hydrophobic than the Cha and AEH substrates, but chymotrypsin showed the highest specificity for this compound. These results demonstrated that the substrate specificity of chymotrypsin is not only affected by the hydrophobicity and aromaticity, but also by the structural expanse of amino acid residues in the substrate.

DOI： 10.3390/pr9020242

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Design and synthesis of a new amphipathic cyclic decapeptide with rapid, stable, and continuous antibacterial effects 査読有り

Farrag H.N., Metwally K., Ikeno S., Kato T.

Pertanika Journal of Science and Technology 28 ( Special issue 2 ) 183 - 196 2020年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Pathogens can acquire high resistance against even the most powerful antibiotics because of the long periods of treatment and high usage of antimicrobial agents. In addition, the severe side effects of commonly used antibiotics can initiate secondary diseases or may lead to death. Antimicrobial peptides (AMPs) have been reported to exhibit prokaryotic selectivity and low microbial resistance. Furthermore, AMPs show a good ability to penetrate the cell walls of microorganisms. In this study, a cyclic decapeptide and its linear counterpart were synthesized by a standard solid phase peptide synthesis method (SPPS) in a quantitative yield of the linear decapeptide (97%) and a good yield of the cyclic form (45%). Antibacterial studies were performed using Escherichia coli (a widespread Gram-negative pathogen) and Bacillus thuringiensis as a representative Gram-positive pathogen. The minimal inhibitory concentration (MIC) values were evaluated by the broth microdilution method. The cyclic peptide and its linear counterpart exhibited MIC values of 0.16 and 0.3 mg/mL, respectively, against Escherichia coli. Against Bacillus thuringiensis, the peptides had the same MIC value of 0.24 mg/mL. Time-kill studies were performed using E. coli, which indicated a fast killing effect of both peptides (≥ 99% of the bacterial cells) after 1 h of incubation using a concentration of two times the MIC value for each peptide. Moreover, bacterial cell viability studies against E. coli carried out using a high bacterial concentration showed that both peptides have a maximum killing effect of more than 80% of the tested bacterial cells.

DOI： 10.47836/pjst.28.S2.15

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Dual emissive bispyrene peptide probes for highly sensitive measurements of trypsin activity and evaluation of trypsin inhibitors 査読有り

Sato D., Kondo T., Kato T.

Bioorganic and Medicinal Chemistry 26 ( 12 ) 3468 - 3473 2018年07月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

© 2018 Elsevier Ltd Peptide substrates were double labeled with pyrenes to prepare fluorescent probes for highly sensitive detection of protease activity and evaluation of protease inhibitors using pyrene monomer/excimer signals. Two proximate pyrene moieties formed excited state dimers in the probes, and these pyrene excimer formations were dissociated by tryptic digestion. The specificity constant of the optimum bispyrene peptide probe was 2.7 times higher than that of the conventional peptide-4-methylcoumarin amide. Moreover, our probe had high sensitivity with an estimated detection limit for trypsin of 4.11 pM. The half maximal inhibitory concentration and dissociation constant of the Bowman–Birk inhibitor were successfully estimated.

DOI： 10.1016/j.bmc.2018.05.021

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Photophysical Characterization and BSA Interaction of Direct Ring Carboxy Functionalized Symmetrical squaraine Dyes 査読有り

Saikiran M., Pandey S., Hayase S., Kato T.

Journal of Physics: Conference Series 924 ( 1 ) 2017年12月

担当区分：最終著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

© Published under licence by IOP Publishing Ltd. A series of far-red sensitive symmetrical squaraine dyes bearing direct-COOH functionalized indole ring were synthesized, characterized and subjected to photophysical investigations. These symmetrical squaraine dyes were then subjected to investigate their interaction with bovine serum albumin (BSA) in Phosphate buffer solutions. All the squaraine dyes under investigation exhibit intense and sharp optical absorption mainly in the far-red wavelength region from 550 nm-700 nm having very high molar extinction coefficients from 1.3 × 10 5 dm 3 .mol -1 .cm -1 . A very small Stokes shift of 10-17 nm indicates the rigid conformational structure of squaraine chromophore. Interaction of these dyes with BSA leads to not only enhanced emission intensity but also bathochromically shifted absorption maximum due to formation of dye-BSA conjugate. These dyes bind strongly with BSA having about an order of magnitude higher binding constant as compared to the reported squaraine dyes. Amongst the symmetrical squaraine dyes investigated in this work one bearing substituents like trifluorobutyl as alkyl chain at N-position of indole ring and carboxylic acid on benzene ring at the terminal (SQ-26) exhibited highest association with the BSA having very high binding constant 8.01 × 10 6 M -1 .

DOI： 10.1088/1742-6596/924/1/012006

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Efficient near infrared fluorescence detection of elastase enzyme using peptide-bound unsymmetrical squaraine dye 査読有り

Saikiran M., Sato D., Pandey S., Hayase S., Kato T.

Bioorganic and Medicinal Chemistry Letters 27 ( 17 ) 4024 - 4029 2017年06月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Extended wavelength analyte-responsive fluorescent probes are highly desired for the imaging applications owing to their deep tissue penetration, and minimum interference from autofluorescence by biomolecules. Near infra-red (NIR) sensitive and self-quenching fluorescent probe based on the dye-peptide conjugate (SQ 1 PC) was designed and synthesized by facile and efficient one-pot synthetic route for the detection of Elastase activity. In the phosphate buffer solution, there was an efficient quenching of fluorescence of SQ 1 PC (86%) assisted by pronounced dye-dye interaction due to H-aggregate formation. Efficient and fast recovery of this quenched fluorescence of SQ 1 PC (> 50% in 30 s) was observed on hydrolysis of this peptide-dye conjugate by elastase enzyme. Presently designed NIR sensitive self-quenching substrate offers the potential application for the detection of diseases related to proteases by efficient and fast detection of their activities.

DOI： 10.1016/j.bmcl.2017.07.057

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