1qhe
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(New page: 200px<br /><applet load="1qhe" size="450" color="white" frame="true" align="right" spinBox="true" caption="1qhe, resolution 2.0Å" /> '''ENERGETICS OF A HYDRO...)
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Revision as of 22:34, 20 November 2007
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ENERGETICS OF A HYDROGEN BOND (CHARGED AND NEUTRAL) AND OF A CATION-PI INTERACTION IN APOFLAVODOXIN
Overview
Anabaena apoflavodoxin contains a single histidine residue (H34) that, interacts with two aromatic residues (F7 and Y47). The histidine and, phenylalanine rings are almost coplanar and they can establish a cation-pi, interaction when the histidine is protonated. The histidine and tyrosine, side-chains are engaged in a hydrogen bond, which is their only contact., We analyse the energetics of these interactions using p Ka-shift analysis, double-mutant cycle analysis at two pH values, and X-ray crystallography., The H/F interaction is very weak when the histidine is neutral, but it is, strengthened by 0.5 kcal mol-1on histidine protonation. Supporting this, fact, the histidine p Kain a F7L mutant is 0.4 pH units lower than in, wild-type. The strength of the H/Y hydrogen bond is 0.7 kcal mol-1when the, histidine is charged, and it becomes stronger (1.3 kcal mol-1) when the, histidine is neutral. This is consistent with our observation that the, (H34)Nepsilon2-OH(Y47) distance is slightly shorter in the apoflavodoxin, structure at pH 9.0 than in the previously reported structure at pH 6.0., It is also consistent with a histidine p Kavalue 0.6 pH units higher in a, Y47F mutant than in the wild-type protein. We suggest that the higher, stability of the neutral hydrogen bond could be due to a higher, desolvation penalty of the charged hydrogen bond that would offset its, more favourable enthalpy of formation. The relationship between hydrogen, bond strength and the contribution of hydrogen bonds to protein stability, is discussed.
About this Structure
1QHE is a Single protein structure of sequence from Anabaena sp. with SO4 as ligand. Full crystallographic information is available from OCA.
Reference
Energetics of a hydrogen bond (charged and neutral) and of a cation-pi interaction in apoflavodoxin., Fernandez-Recio J, Romero A, Sancho J, J Mol Biol. 1999 Jul 2;290(1):319-30. PMID:10388575
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