Structural insights into the role of the cyclic backbone in a squash trypsin inhibitor

Daly, Norelle L., Thorstholm, Louise, Greenwood, Kathryn P., King, Gordon J., Rosengren, K. Johan, Heras, Begoña, Martin, Jennifer L., and Craik, David J. (2013) Structural insights into the role of the cyclic backbone in a squash trypsin inhibitor. Journal of Biological Chemistry, 288 (50). pp. 36141-36148.

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MCoTI-II is a head-to-tail cyclic peptide with potent trypsin inhibitory activity and, on the basis of its exceptional proteolytic stability, is a valuable template for the design of novel drug leads. Insights into inhibitor dynamics and interactions with biological targets are critical for drug design studies, particularly for protease targets. Here, we show that the cyclization and active site loops of MCoTI-II are flexible in solution, but when bound to trypsin, the active site loop converges to a single well defined conformation. This finding of reduced flexibility on binding is in contrast to a recent study on the homologous peptide MCoTI-I, which suggested that regions of the peptide are more flexible upon binding to trypsin. We provide a possible explanation for this discrepancy based on degradation of the complex over time. Our study also unexpectedly shows that the cyclization loop, not present in acyclic homologues, facilitates potent trypsin inhibitory activity by engaging in direct binding interactions with trypsin.

Item ID: 31678
Item Type: Article (Research - C1)
ISSN: 1083-351X
Keywords: NMR, peptide conformation, peptide interactions, protease inhibitor, structural biology, cyclic peptides, cyclotides
Funders: Australian Research Council (ARC), National Health and Medical Research Council (NHMRC)
Projects and Grants: ARC FL0992138, NHMRC APP1026501
Date Deposited: 26 Feb 2014 09:35
FoR Codes: 11 MEDICAL AND HEALTH SCIENCES > 1101 Medical Biochemistry and Metabolomics > 110106 Medical Biochemistry: Proteins and Peptides (incl Medical Proteomics) @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970111 Expanding Knowledge in the Medical and Health Sciences @ 100%
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