title: Disulfide bond mutagenesis and the structure and function of the head-to-tail macrocyclic trypsin inhibitor SFTI-1.
abstract: SFTI-1 is a novel 14 amino acid peptide comprised of a circular backbone constrained by three proline residues, a hydrogen-bond network, and a single disulfide bond. It is the smallest and most potent known Bowman-Birk trypsin inhibitor and the only one with a cyclic peptidic backbone. The solution structure of [ABA(3,11)]SFTI-1, a disulfide-deficient analogue of SFTI-1, has been determined by (1)H NMR spectroscopy. The lowest energy structures of native SFTI-1 and [ABA(3,11)]SFTI-1 are similar and superimpose with a root-mean-square deviation over the backbone and heavy atoms of 0.26 +/- 0.09 and 1.10 +/- 0.22 A, respectively. The disulfide bridge in SFTI-1 was found to be a minor determinant for the overall structure, but its removal resulted in a slightly weakened hydrogen-bonding network. To further investigate the role of the disulfide bridge, NMR chemical shifts for the backbone H(alpha) protons of two disulfide-deficient linear analogues of SFTI-1, [ABA(3,11)]SFTI-1[6,5] and [ABA(3,11)]SFTI-1[1,14] were measured. These correspond to analogues of the cleavage product of SFTI-1 and a putative biosynthetic precursor, respectively. In contrast with the cyclic peptide, it was found that the disulfide bridge is essential for maintaining the structure of these open-chain analogues. Overall, the hydrogen-bond network appears to be a crucial determinant of the structure of SFTI-1 analogues.
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Michael L J
authors.initials: ML
authors.lastname: Korsinczky
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Clark
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D001549:Benzamides / Q000737:chemistry; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry*; D006368:Helianthus; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics*; D017433:Protein Structure, Secondary; D012996:Solutions; D013329:Structure-Activity Relationship; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry* / Q000235:genetics*
chemical_list: D001549:Benzamides; D004220:Disulfides; D010456:Peptides, Cyclic; C448501:SFTI-1 peptide, sunflower; D012996:Solutions; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; C025160:3-aminobenzamide