PMID:9778348

Citation	Stout, TJ, Schellenberger, U, Santi, DV and Stroud, RM (1998) Crystal structures of a unique thermal-stable thymidylate synthase from Bacillus subtilis. Biochemistry 37:14736-47
Abstract	Unlike all other organisms studied to date, Bacillus subtilis expresses two different thymidylate synthases: bsTS-A and bsTS-B. bsTS-A displays enhanced enzymatic and structural thermal stability uncharacteristic of most TSs. Despite the high level of TS conservation across most species, bsTS-A shares low sequence identity (<40%) with the majority of TSs from other organisms. This TS and the TSs from Lactococcus lactis and phage Phi3T-to which it is most similar-have been of interest for some time since, by structure-based sequence alignment, they appear to lack several key residues shown by mutagenesis to be essential to enzymatic function [Greene, P. J., Yu, P. L., Zhao, J., Schiffer, C. A., and Santi, D. (1994) Protein Sci. 3, 1114-6]. In addition, bsTS-A demonstrates specific activity 2-3-fold higher than TS from Lactobacillus casei or Escherichia coli. We have solved the crystal structure of this unusual TS in four crystal forms to a maximum resolution of 1.7 A. Each of these crystal forms contains either one or two noncrystallographically related dimers. Stabilization of the beta-sheet dimer interface through a dramatic architecture of buttressed internal salt bridges maintains the structural integrity of bsTS-A at elevated temperatures. Melting curves of TSs from L. casei and E. coli are compared to that of TS-A from B. subtilis and correlated with numbers of hydrogen bonds, salt bridges, and the numbers of interactions localized to the dimer interface. Analysis of this structure will shed light on the conservation of function across diversity of sequence, as well as provide insights into the thermal stabilization of a highly conserved enzyme.
Links	PubMed Online version:10.1021/bi981270l
Keywords	Amino Acid Sequence; Bacillus subtilis/enzymology; Crystallization; Crystallography, X-Ray; Enzyme Stability; Escherichia coli/genetics; Hot Temperature; Isoenzymes/chemistry; Models, Molecular; Molecular Sequence Data; Recombinant Proteins/biosynthesis; Recombinant Proteins/isolation & purification; Sequence Homology, Amino Acid; Solutions; Thymidylate Synthase/chemistry; Thymidylate Synthase/genetics; Thymidylate Synthase/isolation & purification
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BACSU:TYSY1		GO:0004799: thymidylate synthase activity	ECO:0000314:		F		"Activity assays indicate that bsTS-A has a significantly higher specific activity (SA ≈ 22 units/mg) than either E. coli TS (SA ∼13.5 units/mg) or L. casei TS (SA ≈ 6 units/mg) when measured using the identical materials and instruments." Data not shown.	complete CACAO 11501

References

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