1dx9
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(New page: 200px<br /><applet load="1dx9" size="450" color="white" frame="true" align="right" spinBox="true" caption="1dx9, resolution 2.05Å" /> '''W57A APOFLAVODOXIN F...)
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Revision as of 11:32, 20 November 2007
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W57A APOFLAVODOXIN FROM ANABAENA
Overview
Many flavoproteins are non-covalent complexes between FMN and an, apoprotein. To understand better the stability of flavoproteins, we have, studied the energetics of the complex between FMN and the apoflavodoxin, from Anabaena PCC 7119 by a combination of site-directed mutagenesis, titration calorimetry, equilibrium binding constant determinations, and, x-ray crystallography. Comparison of the strength of the wild type and, mutant apoflavodoxin-FMN complexes and that of the complexes between wild, type apoflavodoxin and shortened FMN analogues (riboflavin and lumiflavin), allows the dissection of the binding energy into contributions associated, with the different parts of the FMN molecule. The estimated contribution, of the phosphate is greatest, at 7 kcal mol(-1); that of the isoalloxazine, is of around 5-6 kcal mol(-1) (mainly due to interaction with Trp-57 and, Tyr-94 in the apoprotein) and the ribityl contributes least: around 1 kcal, mol(-1). The stabilization of the complex is both enthalpic and entropic, although the enthalpy contribution is dominant. Both the phosphate and the, isoalloxazine significantly contribute to the enthalpy of binding. The, ionic strength does not have a large effect on the stability of the FMN, complex because, although it weakens the phosphate interactions, it, strengthens the isoalloxazine-protein hydrophobic interactions. Phosphate, up to 100 mM does not affect the strength of the riboflavin complex, which, suggests the isoalloxazine and phosphate binding sites may be independent, in terms of binding energy. Interestingly, we find crystallographic, evidence of flexibility in one of the loops (57-62) involved in, isoalloxazine binding.
About this Structure
1DX9 is a Single protein structure of sequence from Anabaena sp. with SO4 as ligand. Full crystallographic information is available from OCA.
Reference
Dissecting the energetics of the apoflavodoxin-FMN complex., Lostao A, El Harrous M, Daoudi F, Romero A, Parody-Morreale A, Sancho J, J Biol Chem. 2000 Mar 31;275(13):9518-26. PMID:10734100
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