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

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Abstract
The methyl-accepting chemotaxis proteins (MCP) of E. coli undergo reversible methylation that is 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 2 tryptic peptides, denoted K1 and R1. A second modification of the MCP, which is not methylation, was 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. Partial amino acid sequence analyses were performed on radiolabeled peptides K1 and R1 derived from MCPI and several methyl-accepting sites were identified. In the absence of CheB-dependent modification, a site in peptide K1 is unable to accept methyl gorups. Correlation of this protein sequence data with the nucleotide sequence of the tsr gene 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.