Enzymatic deamidation of methyl-accepting chemotaxis proteins in Escherichia coli catalyzed by the cheB gene product.

The methyl-accepting chemotaxis proteins (MCPs) of Escherichia coli undergo reversible methylation that has been correlated with adaptation of cells to environmental stimuli. MCPI, the product of the tsr gene, accepts methyl groups at multiple sites that are located on two tryptic peptides, denoted K1 and R1. A second modification of the MCPs, which is not methylation, has been designated the CheB-dependent modification. A CheB-dependent modification occurs on methyl-accepting peptide K1 and allows additional methyl groups to be incorporated into this peptide. We have performed partial amino acid sequence analyses on radiolabeled peptides K1 and R1 derived from MCPI and have identified several methyl-accepting sites. We found that, in the absence of CheB-dependent modification, a site in peptide K1 is unable to accept methyl groups. Correlation of this protein sequence data with the nucleotide sequence of the tsr gene [Boyd, A., Kendall, K. & Simon, M.I. (1983) Nature (London) 301, 623-626] suggests that CheB-dependent modification of MCPI is the enzymatic deamidation of glutamine to methyl-accepting glutamic acid. Possible roles for this deamidation in bacterial chemotaxis are discussed.