1o8y

SOLUTION STRUCTURE OF SFTI-1(6,5), AN ACYCLIC PERMUTANT OF THE PROTEINASE INHIBITOR SFTI-1, TRANS-TRANS-TRANS CONFORMER (TT-A)

spinqualitylabelsall models 1o8y, 20 NMR models Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 1o8y is a 1 chain structure. Full experimental information is available from OCA. For a guided tour on the structure components use FirstGlance. Related: 1jbl, 1jbn, 1o8z, 1sfi Resources: FirstGlance, OCA, RCSB, PDBsum Publication Abstract from PubMed The most potent known naturally occurring Bowman-Birk inhibitor, sunflower trypsin inhibitor-1 (SFTI-1), is a bicyclic 14-amino acid peptide from sunflower seeds comprising one disulfide bond and a cyclic backbone. At present, little is known about the cyclization mechanism of SFTI-1. We show here that an acyclic permutant of SFTI-1 open at its scissile bond, SFTI-1[6,5], also functions as an inhibitor of trypsin and that it can be enzymatically backbone-cyclized by incubation with bovine beta-trypsin. The resulting ratio of cyclic SFTI-1 to SFTI-1[6,5] is approximately 9:1 regardless of whether trypsin is incubated with SFTI-1[6,5] or SFTI-1. Enzymatic resynthesis of the scissile bond to form cyclic SFTI-1 is a novel mechanism of cyclization of SFTI-1[6,5]. Such a reaction could potentially occur on a trypsin affinity column as used in the original isolation procedure of SFTI-1. We therefore extracted SFTI-1 from sunflower seeds without a trypsin purification step and confirmed that the backbone of SFTI-1 is indeed naturally cyclic. Structural studies on SFTI-1[6,5] revealed high heterogeneity, and multiple species of SFTI-1[6,5] were identified. The main species closely resembles the structure of cyclic SFTI-1 with the broken binding loop able to rotate between a cis/trans geometry of the I7-P8 bond with the cis conformer being similar to the canonical binding loop conformation. The non-reactive loop adopts a beta-hairpin structure as in cyclic wild-type SFTI-1. Another species exhibits an iso-aspartate residue at position 14 and provides implications for possible in vivo cyclization mechanisms. Enzymatic cyclization of a potent bowman-birk protease inhibitor, sunflower trypsin inhibitor-1, and solution structure of an acyclic precursor peptide.,Marx UC, Korsinczky ML, Schirra HJ, Jones A, Condie B, Otvos L Jr, Craik DJ J Biol Chem. 2003 Jun 13;278(24):21782-9. Epub 2003 Mar 5. PMID:12621047 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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