title: Solution structure of a novel C2-symmetrical bifunctional bicyclic inhibitor based on SFTI-1.
abstract: A novel bifunctional bicyclic inhibitor has been created that combines features both from the Bowman-Birk inhibitor (BBI) proteins, which have two distinct inhibitory sites, and from sunflower trypsin inhibitor-1 (SFTI-1), which has a compact bicyclic structure. The inhibitor was designed by fusing together a pair of reactive loops based on a sequence derived from SFTI-1 to create a backbone-cyclized disulfide-bridged 16-mer peptide. This peptide has two symmetrically spaced trypsin binding sites. Its synthesis and biological activity have been reported in a previous communication [Jaulent and Leatherbarrow, 2004, PEDS 17, 681]. In the present study we have examined the three-dimensional structure of the molecule. We find that the new inhibitor, which has a symmetrical 8-mer half-cystine CTKSIPP'I' motif repeated through a C2 symmetry axis also shows a complete symmetry in its three-dimensional structure. Each of the two loops adopts the expected canonical conformation common to all BBIs as well as SFTI-1. We also find that the inhibitor displays a strong and unique structural identity, with a notable lack of minor conformational isomers that characterise most reactive site loop mimics examined to date as well as SFTI-1. This suggests that the presence of the additional cyclic loop acts to restrict conformational mobility and that the deliberate introduction of cyclic symmetry may offer a general route to locking the conformation of beta-hairpin structures.
authors.affiliation: Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK.
authors.forename: Agnès M
authors.initials: AM
authors.lastname: Jaulent
authors.forename: Arnd B E
authors.initials: AB
authors.lastname: Brauer
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Matthews
authors.forename: Robin J
authors.initials: RJ
authors.lastname: Leatherbarrow
mesh_terms: D006368:Helianthus; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry*; D014361:Trypsin Inhibitors / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D010456:Peptides, Cyclic; C448501:SFTI-1 peptide, sunflower; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; D014361:Trypsin Inhibitors