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Title: Structure and mechanism of soybean ATP sulfurylase and the committed step in plant sulfur assimilation

item HERMANN, JONATHAN - Washington University
item RAVILIOUS, GEOFFREY - Washington University
item MCKINNEY, SAMUEL - Washington University
item WESTFALL, COREY - Washington University
item LEE, SOON GOO - Washington University
item BARANIECKA, PATRYCJA - John Innes Center
item GIOVANNETTI, MARCO - John Innes Center
item STANISLAV, KOPRIVA - John Innes Center
item Krishnan, Hari
item JOSEPH, JEZ - Washington University

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2014
Publication Date: 4/11/2014
Publication URL:
Citation: Hermann, J., Ravilious, G.E., Mckinney, S.E., Westfall, C.S., Lee, S., Baraniecka, P., Giovannetti, M., Stanislav, K., Krishnan, H.B., Joseph, J.M. 2014. Structure and mechanism of soybean ATP sulfurylase and the committed step in plant sulfur assimilation. Journal of Biological Chemistry. 289(15):10919-10929.

Interpretive Summary: Soybean is a rich source of protein. Unfortunately, soybean proteins contain low amounts of two important amino acids, methionine and cysteine, that are vital for optimal growth of humans and animals. Therefore, attempts are being made to increase the amount of these two amino acids in soybeans by manipulating enzymes invloved in sulfur assimilation. ATP sulfurylase catalyzes the energetically unfavorable formation of adenosine-5’-phosphosulfate in plant sulfur assimilation. In this study, we have determined the three-dimensional structure of soybean ATP sulfurylase. Our results provide new molecular insight on the structural evolution of this enzyme in plants and how this enzyme functions as the committed step in plant sulfur assimilation.The information obtained from this study will help biotechnologists to genetically manipulate the sulfur-assimilatory pathway so that we can improve the overall quality of soybean seed proteins. Superior quality soy proteins can be utilized to meet the nutritional requirements of the multitude of malnourished people around the world.

Technical Abstract: Enzymes of the sulfur assimilation pathway are potential targets for improving nutrient content and environmental stress responses in plants. The committed step in this pathway is catalyzed by ATP sulfurylase, which synthesizes adenosine-5'-phosphosulfate (APS) from sulfate and ATP. To better understand the molecular basis of this energetically unfavorable reaction, the 2.48 Å resolution x-ray crystal structure of ATP sulfurylase from soybean (GmATPS) in complex with APS was determined. This structure revealed several highly conserved substrate-binding motifs in the active site and a distinct dimerization interface compared to other ATP sulfurylases. Steady-state kinetic analysis of twenty GmATPS point mutants suggests a reaction mechanism in which nucleophilic attack by sulfate on the a-phosphate of ATP requires bending of the nucleotide phosphate backbone into a "U"-shape and stabilization of the transition state by Arg248, Asn249, His255, and Arg349. This analysis indicates that ATP sulfurylase overcomes the energetic barrier of APS synthesis by distorting nucleotide structure and identifies critical residues for catalysis. Mutations that alter sulfate assimilation in Arabidopsis were mapped to the structure and provide a molecular basis for understanding their effects on the sulfur assimilation pathway.