The Bowman-Birk inhibitor reactive site loop sequence represents an independent structural beta-hairpin motif.
We have determined the NMR structure in aqueous solution of a disulphide-cyclised 11-residue peptide that forms a stable beta-hairpin, incorporating a type VIb beta-turn. The structure is found to be extremely well ordered for a short peptide, with the 30 lowest energy simulated annealing structures having an average pairwise r.m.s. deviation of only 0.36 A over the backbone. All but three side-chains adopt distinct conformations, allowing a detailed analysis of their involvement in cross-strand interactions. The peptide sequence analysed originates from a previously reported study, which identified potent inhibitors of human leukocyte elastase from screening a combinatorial peptide library based on the short protein beta-sheet segment that forms the reactive site loop of Bowman-Birk inhibitors. A detailed comparison of the peptide's solution structure with the corresponding region in the whole protein structure reveals a very good correspondence not only for the backbone (r.m.s. deviation approximately 0.7 A) but also for the side-chains. This isolated beta-hairpin retains the biologically active "canonical conformation" typical of small serine proteinase inhibitor proteins, which explains why it retains inhibitory activity. Since the structural integrity is sequence-inherent and does not depend upon the presence of the remaining protein, this beta-hairpin represents an independent structural motif and so provides a useful model of this type of protein architecture and its relation to biological function. The relationship between the conformation of this beta-hairpin and its biological activity is discussed.
Department of Chemistry, Imperial College of Science Technology and Medicine, South Kensington, London, UK.
A B
AB
Brauer
G
G
Kelly
J D
JD
McBride
R M
RM
Cooke
S J
SJ
Matthews
R J
RJ
Leatherbarrow
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D006860:Hydrogen Bonding; D019272:Leukocyte Elastase / Q000037:antagonists & inhibitors; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D017433:Protein Structure, Secondary; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D014361:Trypsin Inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology
D009842:Oligopeptides; D010446:Peptide Fragments; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; D014361:Trypsin Inhibitors; D019272:Leukocyte Elastase