1qlq
From Proteopedia
|
BOVINE PANCREATIC TRYPSIN INHIBITOR (BPTI) MUTANT WITH ALTERED BINDING LOOP SEQUENCE
Overview
A mutant of bovine pancreatic trypsin inhibitor (BPTI) has been, constructed and expressed in Escherichia coli in order to probe the, kinetic and structural consequences of truncating the binding loop, residues to alanine. In addition to two such mutations (Thr11Ala and, Pro13Ala), it has a conservative Lys15Arg substitution at position P(1), and an unrelated Met52Leu change. In spite of the binding loop, modification, the affinity for trypsin is only 30 times lower than that of, the wild-type protein. At pH 7.5 the protein can be crystallized on the, time-scale of hours, yielding very stable crystals of a new (tetragonal), form of BPTI. Conventional source X-ray data collected to 1.4 A at room, temperature allowed anisotropic structure refinement characterized by, R=0.1048. The structure reveals all 58 residues, including the complete C, terminus, which is in a salt-bridge contact with the N terminus. The, Cys14-Cys38 disulfide bridge is observed in two distinct chiralities. This, bridge, together with an internal water molecule, contributes to the, stabilization of the binding loop. The Ala mutations have only an, insignificant and localized effect on the binding loop, which retains its, wild-type conformation (maximum deviation of loop C(alpha) atoms of 0.7 A, at Ala13). Four (instead of the typical three) additional water molecules, are buried in an internal cleft and connected to the surface via a sulfate, anion. Three more SO(4)(2-) anions are seen in the electron density, one, of them located on a 2-fold axis. It participates in the formation of a, dimeric structure between symmetry-related BPTI molecules, in which, electrostatic and hydrogen bonding interactions resulting from the mutated, Lys15Arg substitution are of central importance. This dimeric interaction, involves direct recognition loop-recognition loop contacts, part of which, are hydrophobic interactions of the patches created by the alanine, mutations. Another 2-fold symmetric interaction between the BPTI molecules, involves the formation of an antiparallel intermolecular beta-sheet that, together with the adjacent intramolecular beta-hairpin loops, creates a, four-stranded structure.
About this Structure
1QLQ is a Single protein structure of sequence from Bos taurus with SO4 as ligand. Full crystallographic information is available from OCA.
Reference
High-resolution structure of bovine pancreatic trypsin inhibitor with altered binding loop sequence., Czapinska H, Otlewski J, Krzywda S, Sheldrick GM, Jaskolski M, J Mol Biol. 2000 Feb 4;295(5):1237-49. PMID:10653700
Page seeded by OCA on Wed Nov 21 00:48:07 2007
