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Updated: Aug 13, 2026

A Purification and In Vitro Activity Assay for a (p)ppGpp Synthetase from Clostridium difficile
Published on: November 3, 2018
Molecular basis for G protein control of the prokaryotic ATP sulfurylase
Joseph D Mougous1, Dong H Lee, Sarah C Hubbard
1Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, California 94720, USA.
Abstract:
Sulfate assimilation is a critical component of both primary and secondary metabolism. An essential step in this pathway is the activation of sulfate through adenylation by the enzyme ATP sulfurylase (ATPS), forming adenosine 5'-phosphosulfate (APS). Proteobacterial ATPS overcomes this energetically unfavorable reaction by associating with a regulatory G protein, coupling the energy of GTP hydrolysis to APS formation. To discover the molecular basis of this unusual role for a G protein, we biochemically characterized and solved the X-ray crystal structure of a complex between Pseudomonas syringae ATPS (CysD) and its associated regulatory G protein (CysN). The structure of CysN*D shows the two proteins in tight association; however, the nucleotides bound to each subunit are spatially segregated. We provide evidence that conserved switch motifs in the G domain of CysN allosterically mediate interactions between the nucleotide binding sites. This structure suggests a molecular mechanism by which conserved G domain architecture is used to energetically link GTP turnover to the production of an essential metabolite.
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