6rsa
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(New page: 200px<br /><applet load="6rsa" size="450" color="white" frame="true" align="right" spinBox="true" caption="6rsa, resolution 2.0Å" /> '''NUCLEAR MAGNETIC RESO...)
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Revision as of 13:18, 20 November 2007
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NUCLEAR MAGNETIC RESONANCE AND NEUTRON DIFFRACTION STUDIES OF THE COMPLEX OF RIBONUCLEASE*A WITH URIDINE VANADATE, A TRANSITION-STATE ANALOGUE
Overview
The complex of ribonuclease A (RNase A) with uridine vanadate (U-V), a, transition-state analogue, has been studied with 51V and proton NMR, spectroscopy in solution and by neutron diffraction in the crystalline, state. Upon the addition of aliquots of U-V at pH 6.6, the C epsilon-H, resonances of the two active-site histidine residues 119 and 12 decrease, in intensity while four new resonances appear. Above pH 8 and below pH 5, these four resonances decrease in intensity as the complex dissociates., These four resonances are assigned to His-119 and His-12 in protonated and, unprotonated forms in the RNase-U-V complex. These resonances do not, titrate or change in relative area in the pH range 5-8, indicating a slow, protonation process, and the extent of protonation remains constant with, ca. 58% of His-12 and ca. 26% of His-119 being protonated. The results of, diffraction studies show that both His-12 and His-119 occupy well-defined, positions in the RNase-U-V complex and that both are protonated. However, while the classic interpretation of the mechanism of action of RNase based, on the proposal of Findlay et al. [Findlay, D., Herries, D. G., Mathias, A. P., Rabin, B. R., & Ross, C. A. (1962) Biochem. J. 85, 152-153], requires both His-12 and His-119 to be in axial positions relative to the, pentacoordinate transition state, in the diffraction structure His-12 is, found to be in an equatorial position, while Lys-41 is close to an axial, position. Hydrogen exchange data show that the mobility and accessibility, of amides in the RNase-U-V complex do not significantly differ from what, was observed in the native enzyme. The results of both proton NMR in, solution and neutron diffraction in the crystal are compared and, interpreted in terms of the mechanism of action of RNase.
About this Structure
6RSA is a Single protein structure of sequence from Bos taurus with UVC and DOD as ligands. Active as Pancreatic ribonuclease, with EC number 3.1.27.5 Full crystallographic information is available from OCA.
Reference
Nuclear magnetic resonance and neutron diffraction studies of the complex of ribonuclease A with uridine vanadate, a transition-state analogue., Borah B, Chen CW, Egan W, Miller M, Wlodawer A, Cohen JS, Biochemistry. 1985 Apr 9;24(8):2058-67. PMID:4016100
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