1FPM

MONOVALENT CATION BINDING SITES IN N10-FORMYLTETRAHYDROFOLATE SYNTHETASE FROM MOORELLA THERMOACETICA

Summary for 1FPM

• Entry DOI: 10.2210/pdb1fpm/pdb
• Related: 1FP7
• Descriptor: FORMATE--TETRAHYDROFOLATE LIGASE, SULFATE ION, CESIUM ION, ... (4 entities in total)
• Functional Keywords: monovalent cation, thermostable, tetramer, ligase
• Biological source: Moorella thermoacetica
• Total number of polymer chains: 2
• Total formula weight: 120994.18

Authors

Radfar, R.,Leaphart, A.,Brewer, J.M.,Minor, W.,Odom, J.D. (deposition date: 2000-08-31, release date: 2001-08-31, Last modification date: 2024-02-07)

Primary citation

Radfar, R.,Leaphart, A.,Brewer, J.M.,Minor, W.,Odom, J.D.,Dunlap, R.B.,Lovell, C.R.,Lebioda, L.
Cation binding and thermostability of FTHFS monovalent cation binding sites and thermostability of N10-formyltetrahydrofolate synthetase from Moorella thermoacetica.
Biochemistry, 39:14481-14486, 2000

PubMed Abstract: 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.

PubMed: 11087401
DOI: 10.1021/bi001577w

Experimental method

X-RAY DIFFRACTION (3 Å)