The refined 2.0 A X-ray crystal structure of the complex formed between bovine beta-trypsin and CMTI-I, a trypsin inhibitor from squash seeds (Cucurbita maxima). Topological similarity of the squash seed inhibitors with the carboxypeptidase A inhibitor from potatoes.
The stoichiometric complex formed between bovine beta-trypsin and the Cucurbita maxima trypsin inhibitor I (CMTI-I) was crystallized and its X-ray crystal structure determined using Patterson search techniques. Its structure has been crystallographically refined to a final R value of 0.152 (6.0-2.0 A). CMTI-I is of ellipsoidal shape; it lacks helices or beta-sheets, but consists of turns and connecting short polypeptide stretches. The disulfide pairing is CYS-3I-20I, Cys-10I-22I and Cys-16I-28I. According to the polypeptide fold and disulfide connectivity its structure resembles that of the carboxypeptidase A inhibitor from potatoes. Thirteen of the 29 inhibitor residues are in direct contact with trypsin; most of them are in the primary binding segment Val-2I (P4)-Glu-9I (P4') which contains the reactive site bond Arg-5I-Ile-6I and is in a conformation observed also for other serine proteinase inhibitors.
Bode
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Max-Planck-Institut für Biochemie, Martinsried, FRG.
Greyling
H J
HJ
Huber
R
R
Otlewski
J
J
Wilusz
T
T
D000818:Animals; D001665:Binding Sites; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors; D043422:Carboxypeptidases A; D002417:Cattle; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008958:Models, Molecular; D010944:Plants / Q000201:enzymology; D011485:Protein Binding; D011487:Protein Conformation; D014357:Trypsin; D014361:Trypsin Inhibitors
D046911:Macromolecular Substances; D014361:Trypsin Inhibitors; D002268:Carboxypeptidases; D043422:Carboxypeptidases A; D014357:Trypsin