A Protein Methyltransferase Specific for Altered Aspartyl Residues is Important in Escherichia coli Stationary-Phase Survival and Heat-Shock Resistance

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 89; no. 20; pp. 9885 - 9889
• Main Authors: Li, Chuan, Clarke, Steven
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 15.10.1992; National Acad Sciences; National Academy of Sciences
• Subjects: aging; Aspartic Acid - analogs & derivatives; Bacteria; Biochemistry; Biology; Cellular metabolism; DNA; E coli; Enzymes; Escherichia coli; Escherichia coli - enzymology; Escherichia coli - growth & development; Genes; heat shock; Heat treatment; Hot Temperature; metabolism; Mutagenesis, Insertional; Mutation; Open reading frames; Oxidation-Reduction; Plasmids; Protein D-Aspartate-L-Isoaspartate Methyltransferase; Protein Methyltransferases - genetics; Protein Methyltransferases - metabolism; protein-D-aspartate methyltransferase; Proteins; resistance; role; Steepest descent method; Substrate Specificity; Viability
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.89.20.9885

Proteins are subject to spontaneous degradation reactions including the deamidation, isomerization, and racemization of asparaginyl and aspartyl residues. A major product of these reactions, the L-isoaspartyl residue, is recognized with high affinity by the protein-L-isoaspartate(D-aspartate) O-methyltransferase (EC 2.1.1.77). This enzyme catalyzes the methyl esterification of the L-isoaspartyl residue in a reaction that can initiate its conversion to the normal aspartyl configuration. To directly study the physiological role of this methyltransferase, especially with respect to the potential repair of isomerized aspartyl residues in aging proteins, we examined the ability of the bacterium Escherichia coli to survive in the absence of its activity. We utilized gene disruption techniques to replace the chromosomal copy of the pcm gene that encodes the methyltransferase with a kanamycin-resistance cassette to produce mutants that have no detectable L-isoaspartyl methyltransferase activity. Although no changes in exponential-phase growth were observed, pcm-mutants did not survive well upon extended culture into stationary phase or upon heat challenge at 55⚬C. These results provide genetic evidence for a role of the L-isoaspartyl methyltransferase in the metabolism of altered proteins that can accumulate in aging cells and limit their viability.