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Crystal Structure Analysis of the E197betaA Mutant of E. coli SCS
Structural highlights
FunctionSUCD_ECOLI During aerobic metabolism it functions in the citric acid cycle, coupling the hydrolysis of succinyl-CoA to the synthesis of ATP and thus represents an important site of substrate-level phosphorylation. It can also function in the other direction for anabolic purposes, and this may be particularly important for providing succinyl-CoA during anaerobic growth when the oxidative route from 2-oxoglutarate is severely repressed. The alpha-subunit binds CoA, as well as ATP and catalyzes phosphoryl transfer to one of its histidine residues. The complete active site is probably located in the region of alpha-beta contact. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedSuccinyl-CoA synthetase catalyzes the reversible reaction succinyl-CoA + NDP + P(i) <--> succinate + CoA + NTP (N denoting adenosine or guanosine). The enzyme consists of two different subunits, designated alpha and beta. During the reaction, a histidine residue of the alpha-subunit is transiently phosphorylated. This histidine residue interacts with Glu 208 alpha at site I in the structures of phosphorylated and dephosphorylated Escherichia coli SCS. We postulated that Glu 197 beta, a residue in the nucleotide-binding domain, would provide similar stabilization of the histidine residue during the actual phosphorylation/dephosphorylation by nucleotide at site II. In this work, these two glutamate residues have been mutated individually to aspartate or glutamine. Glu 197 beta has been additionally mutated to alanine. The mutant proteins were tested for their ability to be phosphorylated in the forward or reverse direction. The aspartate mutant proteins can be phosphorylated in either direction, while the E208 alpha Q mutant protein can only be phosphorylated by NTP, and the E197 beta Q mutant protein can only be phosphorylated by succinyl-CoA and P(i). These results demonstrate that the length of the side chain at these positions is not critical, but that the charge is. Most significantly, the E197 beta A mutant protein could not be phosphorylated in either direction. Its crystal structure shows large differences from the wild-type enzyme in the conformation of two residues of the alpha-subunit, Cys 123 alpha-Pro 124 alpha. We postulate that in this conformation, the protein cannot productively bind succinyl-CoA for phosphorylation via succinyl-CoA and P(i). Two glutamate residues, Glu 208 alpha and Glu 197 beta, are crucial for phosphorylation and dephosphorylation of the active-site histidine residue in succinyl-CoA synthetase.,Fraser ME, Joyce MA, Ryan DG, Wolodko WT Biochemistry. 2002 Jan 15;41(2):537-46. PMID:11781092[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences | ||||||||||||||||||||
