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Protein Engineering vol. 16 no. 12 pp. 1071-1079, 2003
© 2003 Oxford University Press

Structural and functional analysis of a truncated form of Saccharomyces cerevisiae ATP sulfurylase: C-terminal domain essential for oligomer formation but not for activity

D.J. Lalor1, T. Schnyder1, V. Saridakis2,3, D.E. Pilloff4, A. Dong3, H. Tang1, T.S. Leyh4 and E.F. Pai1,2,3,5

1Department of Biochemistry, 2Medical Biophysics and Molecular & Medical Genetics, University of Toronto, Toronto, Ontario M5S 1A8, 3Molecular and Structural Biology, Ontario Cancer Institute/Princess Margaret Hospital, University Health Network, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada and 4Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461-1926, USA

5 To whom correspondence should be addressed at: Division of Molecular and Structural Biology, Ontario Cancer Institute/Princess Margaret Hospital, University Health Network, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada. e-mail: pai{at}hera.med.utoronto.ca

ATP sulfurylase catalyzes the first step in the activation of sulfate by transferring the adenylyl-moiety (AMP~) of ATP to sulfate to form adenosine 5'-phosphosulfate (APS) and pyrophosphate (PPi). Subsequently, APS kinase mediates transfer of the {gamma}-phosphoryl group of ATP to APS to form 3'-phosphoadenosine 5'-phosphosulfate (PAPS) and ADP. The recently determined crystal structure of yeast ATP sulfurylase suggests that its C-terminal domain is structurally quite independent from the other domains, and not essential for catalytic activity. It seems, however, to dictate the oligomerization state of the protein. Here we show that truncation of this domain results in a monomeric enzyme with slightly enhanced catalytic efficiency. Structural alignment of the C-terminal domain indicated that it is extremely similar in its fold to APS kinase although not catalytically competent. While carrying out these structural and functional studies a surface groove was noted. Careful inspection and modeling revealed that the groove is sufficiently deep and wide, as well as properly positioned, to act as a substrate channel between the ATP sulfurylase and APS kinase-like domains of the enzyme.

Received July 17, 2003; revised October 27, 2003; accepted October 28, 2003


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