The 1.6 A structure of Kunitz-type domain from the alpha 3 chain of human type VI collagen

• Published in: Journal of molecular biology 1995-03, Vol.246 (5), p.609-617
• Main Authors: Arnoux, B, Mérigeau, K, Saludjian, P, Norris, F, Norris, K, Bjørn, S, Olsen, O, Petersen, L, Ducruix, A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Aprotinin - chemistry; Base Sequence; Binding Sites; Collagen - chemistry; Crystallization; Crystallography, X-Ray; Humans; Models, Molecular; Molecular Sequence Data; Peptide Fragments - chemistry; Protein Structure, Secondary; Protein Structure, Tertiary
• ISSN: 0022-2836

The C-terminal Kunitz-type domain from the alpha 3 chain of human type VI collagen (C5), a single 58 amino acid residue chain with three disulfide bridges, was cloned, expressed and crystallized in a monoclonic form, space group P2(1), with a = 25.7 A, b = 38.2 A, c = 28.8 A and beta = 109 degrees. The structure was resolved by molecular replacement, using Alzheimer's protein precursor inhibitor and bovine pancreatic trypsin inhibitor three-dimensional structures as search models. The molecule with one sulfate ion and 43 associated water molecules was refined by XPLOR to an R-factor of 18.9% at 1.6 A. The molecule was not degraded by trypsin and did not inhibit trypsin or tested serine proteases. As opposed to the other Kunitz family members, C5 demonstrates left-handed chirality of the Cys14-Cys38 disulfide bond. Inversion of the Thr13 carbonyl and bulky side-chains at the interface with trypsin in a model of the C5-trypsin complex may explain the lack of inhibition of trypsin.