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The refined 2.0 Å X‐ray crystal structure of the complex formed between bovine β‐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
Author(s) -
Bode Wolfram,
Greyling H.Johann,
Huber Robert,
Otlewski Jacek,
Wilusz Tadeusz
Publication year - 1989
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(89)80486-7
Subject(s) - cucurbita maxima , trypsin inhibitor , squash , trypsin , chemistry , kunitz sti protease inhibitor , crystallography , biology , botany , enzyme , biochemistry
The stoichiometric complex formed between bovine β‐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 Å). CMTI‐I is of ellipsoidal shape; it lacks helices or β‐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.