title: Structure of the two-domain hexameric APS kinase from Thiobacillus denitrificans: structural basis for the absence of ATP sulfurylase activity.
abstract: The Tbd_0210 gene of the chemolithotrophic bacterium Thiobacillus denitrificans is annotated to encode a 60.5 kDa bifunctional enzyme with ATP sulfurylase and APS kinase activity. This putative bifunctional enzyme was cloned, expressed and structurally characterized. The 2.95 A resolution X-ray crystal structure reported here revealed a hexameric assembly with D(3) symmetry. Each subunit contains a large N-terminal sulfurylase-like domain and a C-terminal APS kinase domain reminiscent of the two-domain fungal ATP sulfurylases of Penicillium chrysogenum and Saccharomyces cerevisiae, which also exhibit a hexameric assembly. However, the T. denitrificans enzyme exhibits numerous structural and sequence differences in the N-terminal domain that render it inactive with respect to ATP sulfurylase activity. Surprisingly, the C-terminal domain does indeed display APS kinase activity, indicating that this gene product is a true APS kinase. Therefore, these results provide the first structural insights into a unique hexameric APS kinase that contains a nonfunctional ATP sulfurylase-like domain of unknown function.
authors.affiliation: Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Gay
authors.forename: Irwin H
authors.initials: IH
authors.lastname: Segel
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Fisher
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013430:Sulfate Adenylyltransferase / Q000378:metabolism; D013855:Thiobacillus / Q000201:enzymology*
chemical_list: D017853:Phosphotransferases (Alcohol Group Acceptor); C019617:adenylylsulfate kinase; D013430:Sulfate Adenylyltransferase