MUTATIONAL ANALYSIS OF UMP KINASE FROM ESCHERICHIA-COLI

UMP kinase from Escherichia coli is one of the four regulatory enzymes involved in the de novo biosynthetic pathway of pyrimidine nucleotide s. This homohexamer, with no counterpart in eukarya, might serve as a target for new antibacterial drugs, Although the bacterial enzyme does not show sequence similarity with any other known nucleoside monophos phate kinase, two segments between amino acids 35 to 78 and 145 to 194 exhibit 28% identity with phosphoglycerate kinase and 30% identity wi th aspartokinase, respectively, Based on these similarities, a number of residues of E, coli UMP kinase were selected for site-directed muta genesis experiments. Biochemical, kinetic, and spectroscopic analysis of the modified proteins identified residues essential for catalysis ( Asp146), binding of UMP (Asp174), and interaction with the allosteric effecters, GTP and UTP (Arg62 and Asp77).