1fpm
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(New page: 200px<br /><applet load="1fpm" size="450" color="white" frame="true" align="right" spinBox="true" caption="1fpm, resolution 3.00Å" /> '''MONOVALENT CATION BI...)
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Revision as of 13:00, 20 November 2007
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MONOVALENT CATION BINDING SITES IN N10-FORMYLTETRAHYDROFOLATE SYNTHETASE FROM MOORELLA THERMOACETICA
Overview
Formyltetrahydrofolate synthetase (FTHFS) from the thermophilic, homoacetogen, Moorella thermoacetica, has an optimum temperature for, activity of 55-60 degrees C and requires monovalent cations for both, optimal activity and stabilization of tetrameric structure at higher, temperatures. The crystal structures of complexes of FTHFS with cesium and, potassium ions were examined and monovalent cation binding positions, identified. Unexpectedly, NH(4)(+) and K(+), both of which are strongly, activating ions, bind at a different site than a moderately activating, ion, Cs(+), does. Neither binding site is located in the active site. The, sites are 7 A apart, but in each of them, the side chain of Glu 98, which, is conserved in all known bacterial FTHFS sequences, participates in metal, ion binding. Other ligands in the Cs(+) binding site are four oxygen atoms, of main chain carbonyls and water molecules. The K(+) and NH(4)(+) binding, site includes the carboxylate of Asp132 in addition to Glu98. Mutant, FTHFS's (E98Q, E98D, and E98S) were obtained and analyzed using, differential scanning calorimetry to examine the effect of these mutations, on the thermostability of the enzyme with and without added K(+) ions. The, addition of 0.2 M K(+) ions to the wild-type enzyme resulted in a 10, degrees C increase in the thermal denaturation temperature. No significant, increase was observed in E98D or E98S. The lack of a significant effect of, monovalent cations on the stability of E98D and E98S indicates that this, alteration of the binding site eliminates cation binding. The thermal, denaturation temperature of E98Q was 3 degrees C higher than that of the, wild-type enzyme in the absence of the cation, indicating that the removal, of the unbalanced, buried charge of Glu98 stabilizes the enzyme. These, results confirm that Glu98 is a crucial residue in the interaction of, monovalent cations with FTHFS.
About this Structure
1FPM is a Single protein structure of sequence from Moorella thermoacetica with SO4 and CS as ligands. Active as Formate--tetrahydrofolate ligase, with EC number 6.3.4.3 Full crystallographic information is available from OCA.
Reference
Cation binding and thermostability of FTHFS monovalent cation binding sites and thermostability of N10-formyltetrahydrofolate synthetase from Moorella thermoacetica., Radfar R, Leaphart A, Brewer JM, Minor W, Odom JD, Dunlap RB, Lovell CR, Lebioda L, Biochemistry. 2000 Nov 28;39(47):14481-6. PMID:11087401
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