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Published January 1980 | Published
Journal Article Open

Structure of Potato Inhibitor Complex of Carboxypeptidase A at 5.5Å Resolution

Abstract

The complex of the 39-amino inhibitor (potato) of bovine carboxypeptidase A (carboxypeptidase; peptidyl-L-amino-acid hydrolase, EC 3.4.12.2) was crystallized in space group P3_2. There are two protein-inhibitor complexes in the asymmetric unit. These crystals exhibited pseudo-P32_21 symmetry due to twinning about the a_3 axis. Heavy atom difference Patterson maps and rotation functions indicated, however, that the noncrystallographic twofold axis that relates these two complexes is nearly coincident with the a_3 axis. Consequently, to a good approximation at low resolution, the space group of the complex is P3_221 and the effects of twinning may be ignored. The structure was solved by using multiple isomorphous replacement and molecular replacement techniques. At 5.5-Å resolution, the multiple isomorphous replacement map was readily interpretable in terms of the known native carboxypeptidase A structure plus extra density around the active site. The position of this extra density is consistent with the binding mode for extended substrate proposed from earlier model building studies with the native enzyme (Lipscomb, W.N., Hartsuck, J.A., Reeke, G.N., Quiocho, F.A. Bethge, P.H., Ludwig, M.L., Steitz, T.A., Muirhead, H. & Coppola, J.C. (1968) Brookhaven Symp. Biol. 21, 24-90).

Additional Information

© 1980 National Academy of Sciences. Contributed by William N. Lipscomb, October 18, 1979. We thank H. Wyckoff for advice on data collection and the National Institutes of Health (Grant GM 06920) for support. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S. C. §1734 solely to indicate this fact.

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