1xvj
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(New page: 200px<br /><applet load="1xvj" size="450" color="white" frame="true" align="right" spinBox="true" caption="1xvj, resolution 1.80Å" /> '''Crystal Structure Of...)
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Revision as of 04:15, 21 November 2007
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Crystal Structure Of Rat alpha-Parvalbumin D94S/G98E Mutant
Overview
Simultaneous replacement of Asp-94 with serine and Gly-98 with glutamate, in rat alpha-parvalbumin creates a CD-site ligand array in the context of, the EF-site binding loop. Previous work has shown that, relative to the, wild-type CD site, this engineered site has markedly reduced Ca(2+), affinity. Seeking an explanation for this phenomenon, we have obtained the, crystal structure of the alpha D94S/G98E variant. The Ca(2+) coordination, within the engineered EF site of the 94/98E variant is nearly identical to, that within the CD site, suggesting that the attenuated affinity of the EF, site in 94/98E is not a consequence of suboptimal coordination geometry., We have also examined the divalent ion binding properties of the alpha, 94/98E variant in both Na(+)- and K(+)-containing buffers. Although the, Ca(2+) and Mg(2+) affinities are higher in K(+) solution, the increases, are comparable to those observed for wild-type alpha. Consistent with that, finding, the apparent Na(+) stoichiometry, estimated from stability, studies conducted as a function of Na(+) concentration, is 1.0 +/- 0.1, identical to that of wild-type alpha. Thus, the reduced affinity for, divalent ions is evidently not the result of heightened monovalent ion, competition. The thermodynamic analysis indicates that the less favorable, Gibbs free energy of binding reflects a substantial enthalpic penalty., Significantly, the crystal structure reveals a steric clash between Phe-57, and the C(gamma) atom of Glu-98. The consequent displacement of Phe-57, also produces a close contact with Ser-55. Thus, steric interference may, be the source of the enthalpic penalty.
About this Structure
1XVJ is a Single protein structure of sequence from Rattus norvegicus with CA as ligand. Full crystallographic information is available from OCA.
Reference
Crystal structure of the D94S/G98E variant of rat alpha-parvalbumin. An explanation for the reduced divalent ion affinity., Tanner JJ, Agah S, Lee YH, Henzl MT, Biochemistry. 2005 Aug 23;44(33):10966-76. PMID:16101280
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