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Crystal structure of thymidylate synthase A from Bacillus subtilis

Published online by Cambridge University Press:  01 March 1999

KRISTIN M. FOX
Affiliation:
Department of Chemistry, Union College, Schenectady, New York 12308
FRANK MALEY
Affiliation:
Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Albany, New York 12201
ARAIK GARIBIAN
Affiliation:
Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Albany, New York 12201
LI-MING CHANGCHIEN
Affiliation:
Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Albany, New York 12201
PATRICK VAN ROEY
Affiliation:
Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Albany, New York 12201
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Abstract

Thymidylate synthase (TS) converts dUMP to dTMP by reductive methylation, where 5,10-methylenetetrahydrofolate is the source of both the methylene group and reducing equivalents. The mechanism of this reaction has been extensively studied, mainly using the enzyme from Escherichia coli. Bacillus subtilis contains two genes for TSs, ThyA and ThyB. The ThyB enzyme is very similar to other bacterial TSs, but the ThyA enzyme is quite different, both in sequence and activity. In ThyA TS, the active site histidine is replaced by valine. In addition, the B. subtilis enzyme has a 2.4-fold greater kcat than the E. coli enzyme. The structure of B. subtilis thymidylate synthase in a ternary complex with 5-fluoro-dUMP and 5,10-methylenetetrahydrofolate has been determined to 2.5 Å resolution. Overall, the structure of B. subtilis TS (ThyA) is similar to that of the E. coli enzyme. However, there are significant differences in the structures of two loops, the dimer interface and the details of the active site. The effects of the replacement of histidine by valine and a serine to glutamine substitution in the active site area, and the addition of a loop over the carboxy terminus may account for the differences in kcat found between the two enzymes.

Type
Research Article
Copyright
© 1999 The Protein Society

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