Solution structures by ¹H NMR of the novel cyclic trypsin inhibitor SFTI-1 from sunflower seeds and an acyclic permutant

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• 作者：Korsinczky ; Michael L.J. ; Schirra ; Horst Joachim ; Rosengren ; K. Johan ; West ; Jenny ; Condie ; Barrie A. ; et. al.
• 关键词：circular proteins ; cyclic peptide ; cyclotides ; Bowman-Birk inhibitor ; trypsin inhibitor ; ¹H-NMR ; proton nuclear magnetic resonance ; BAPNA ; Nα ; -benzoyl-l-arginine p-nitroanilide ; BB ; Bowman-Birk ; DQF-COSY ; double quantum filtered 2D correlat
• 刊名：Journal of Molecular Biology
• 出版年：2001
• 出版时间：August 17, 2001
• 年：2001
• 卷：311
• 期：3
• 页码：579-591
• 全文大小：389 K

文摘

SFTI-1 is a recently discovered cyclic peptide trypsin inhibitor from sunflower seeds comprising 14 amino acid residues. It is the most potent known Bowman-Birk inhibitor and the only naturally occurring cyclic one. The solution structure of SFTI-1 has been determined by ¹H-NMR spectroscopy and compared with a synthetic acyclic permutant. The solution structures of both are remarkably similar. The lowest energy structures from each family of 20 structures of cyclic and acyclic SFTI-1 have an rmsd over the backbone and heavy atoms of 0.29 Å and 0.66 Å, respectively. The structures consist of two short antiparallel β-strands joined by an extended loop containing the active site at one end. Cyclic SFTI-1 also has a hairpin turn completing the cycle. Both molecules contain particularly stable arrangements of cross-linking hydrogen bonds between the β-strands and a single disulfide bridge, making them rigid and well defined in solution. These stable arrangements allow both the cyclic and acyclic variants of SFTI-1 to inhibit trypsin with very high potencies (0.5 nM and 12.1 nM, respectively). The cyclic nature of SFTI-1 appears to have evolved to provide higher trypsin inhibition as well as higher stability. The solution structures are similar to the crystal structure of the cyclic inhibitor in complex with trypsin. The lack of a major conformational change upon binding suggests that the structure of SFTI-1 is rigid and already pre-organized for maximal binding due to minimization of entropic losses compared to a more flexible ligand. These properties make SFTI-1 an ideal platform for the design of small peptidic pharmaceuticals or pesticides.