This old version of Proteopedia is provided for student assignments while the new version is undergoing repairs. Content and edits done in this old version of Proteopedia after March 1, 2026 will eventually be lost when it is retired in about June of 2026.
Apply for new accounts at the new Proteopedia. Your logins will work in both the old and new versions.
1ab7
From Proteopedia
|
NMR 15N RELAXATION AND STRUCTURAL STUDIES REVEAL CONFORMATIONAL EXCHANGE IN BARSTAR C40/82A, 30 STRUCTURES
Overview
Barstar an 89-residue protein consisting of four helices and a, three-stranded parallel beta-sheet, is the intracellular inhibitor of the, endoribonuclease barnase. Barstar C40/82A, a mutant in which the two, cysteine residues have been replaced by alanine, has been used as a pseudo, wild-type in folding studies and in the crystal structure of the, barnase:barstar C40/82A complex. We have determined a high resolution, solution structure of barstar C40/82A. The structures of barstar C40/82A, and the wild-type are superimposable. A comparison with the crystal, structure of the barnase:barstar C40/82A complex revealed subtle, differences in the regions involved in the binding of barstar to barnase., Side-chain rotations of residues Asn33, Asp35 and Asp39 and a movement of, the binding loop (Pro27-Glu32) towards the binding site of barnase, facilitate the formation of interface hydrogen bonds and aromatic contacts, in the complex. Extreme line broadening and missing signals in 1H-15N, correlation spectra indicate substantial conformational exchange for a, large subset of residues. 15N relaxation data at two magnetic field, strengths, 11.74 T and 14.10 T, were used to estimate exchange, contributions and to map the spectral density function at five, frequencies: 0, 50, 60, 450 and 540 MHz. Based on these results, model-free calculations with the inclusion of estimated exchange, contributions were used to derive order parameters and internal, correlation times. The validity of this approach has been investigated, with model-free calculations that incorporate longitudinal relaxation, rates and heteronuclear 1H-15N NOE data only at 11.74 T and 14.10 T. The, relaxation data suggest substantial conformational exchange in regions of, barstar C40/82A, including the binding loop, the second and the third, helices, and the second and the third strands. Amide proton exchange, experiments suggest a stable hydrogen bond network for all helices and, sheets except the third helix and the C-terminal of the second and the, third strands. The combined results indicate a rigid body movement of the, second helix and twisting motions of the beta-sheet of barstar, which, might be important for the interaction with barnase.
About this Structure
1AB7 is a Single protein structure of sequence from Bacillus amyloliquefaciens. Structure known Active Site: BNB. Full crystallographic information is available from OCA.
Reference
NMR 15N relaxation and structural studies reveal slow conformational exchange in barstar C40/82A., Wong KB, Fersht AR, Freund SM, J Mol Biol. 1997 May 2;268(2):494-511. PMID:9159486
Page seeded by OCA on Mon Nov 5 15:46:21 2007
