Chymotrypsin inhibitor 2 (CI-2), a serine proteinase inhibitor from barley seeds, has been crystallized and its three-dimensional structure determined at 2.0-A resolution by the molecular replacement method. The structure has been refined by restrained-parameter least-squares methods to a crystallographic R factor (= sigma parallel Fo magnitude of-Fo parallel/sigma magnitude of Fo) o of 0 ...
Chymotrypsin inhibitor 2 (CI-2), a serine proteinase inhibitor from barley seeds, has been crystallized and its three-dimensional structure determined at 2.0-A resolution by the molecular replacement method. The structure has been refined by restrained-parameter least-squares methods to a crystallographic R factor (= sigma parallel Fo magnitude of-Fo parallel/sigma magnitude of Fo) o of 0.198. CI-2 is a member of the potato inhibitor 1 family. It lacks the characteristic stabilizing disulfide bonds of most other members of serine proteinase inhibitor families. The body of CI-2 shows few conformational changes between the free inhibitor and the previously reported structure of CI-2 in complex with subtilisin Novo [McPhalen, C.A., Svendsen, I., Jonassen, I., & James, M.N.G. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7242-7246]. However, the reactive site loop has some significant conformational differences between the free inhibitor and its complexed form. The residues in this segment of polypeptide exhibit relatively large thermal motion parameters and some disorder in the uncomplexed form of the inhibitor. The reactive site bond is between Met-59I and Glu-60I in the consecutive sequential numbering of CI-2 (Met-60-Glu-61 according to the alignment of Svendsen et al. [Svendsen, I., Hejgaard, J., & Chavan, J.K. (1984) Carlsberg Res. Commun. 49, 493-502]). The network of hydrogen bonds and electrostatic interactions stabilizing the conformation of the reactive site loop is much less extensive in the free than in the complexed inhibitor.
Related Citations:
Comparison of the Solution and X-Ray Structures of Barley Serine Proteinase Inhibitor 2 Clore, G.M., Gronenborn, A.M., James, M.N.G., Kjaer, M., Mcphalen, C.A., Poulsen, F.M. (1987) Protein Eng 1: 313
Crystal and Molecular Structure of Chymotrypsin Inhibitor 2 from Barley Seeds in Complex with Subtilisin Novo Mcphalen, C.A., Svendsen, I., Jonassen, I., James, M.N.G. (1985) Proc Natl Acad Sci U S A 82: 7242
Preliminary Crystallographic Data for the Serine Protease Inhibitor Ci-2 from Barley Seeds Mcphalen, C.A., Evans, C., Hayakawa, K., Jonassen, I., Svendsen, I., James, M.N.G. (1983) J Mol Biol 168: 445
Organizational Affiliation:
Department of Biochemistry and Molecular Biology, Center for Structural Biology, McKnight Brain Institute, College of Medicine, University of Florida, Gainesville, FL 32610, USA.
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