Amino acid sequence of Escherichia coli citrate synthase

Abstract

Detailed evidence for the amino acid sequence of allosteric citrate synthase from E. coli is presented. The evidence confirms all but 11 of the residues inferred from the sequence of the gene as reported previously; no information was obtained about 10 of these (residues 101-108 and 217-218), and aspartic acid rather than asparagine was found at position 10. Substantial regions of sequence homology were noted between the E. coli enzyme and citrate synthase from pig heart, especially near residues thought to be involved in the active site. Deletions or insertions must be assumed in a number of places in order to maximize homology. Either of 2 lysines, at positions 355 and 356, could be formally homologous to the trimethyllysine of pig heart enzyme, but neither of these is methylated. Evidently, E. coli and pig heart citrate synthases are formed of basically similar subunits but considerable differences exist, which must explain why the E. coli enzyme is hexameric and allosterically inhibited by NADH, while the pig heart enzyme is dimeric and insensitive to that nucleotide.