12 Reversible methylation of glutamate residues in the receptor proteins of bacterial sensory systems

Receptor density balances signal stimulation and attenuation in membrane-assembled complexes of bacterial chemotaxis signaling proteins

“…1A depicts an E. coli methyl-accepting chemoreceptor dimer (green). The organization of the ligand-binding domain that the major E. coli chemoreceptors typify is the most prevalent organization in a diverse group of sensing domains found among the microbial chemoreceptors (7,29). The c-domain exhibits greater conservation; it is often comprised of a single membrane-proximal HAMP domain (30) connected to the methyl-accepting (MA) signal domain.…”

“…In prokaryotes, the methyl-accepting chemotaxis proteins are widespread; the organization of the E. coli pathway is representative of many, but not all, aspects (7,16). Attractant-induced unclustering of receptor signaling complexes-an important facet of the mechanism-is found in both Grampositive and negative bacteria (23), but variations in signaling logic imply that density dependences will be implemented in different ways.…”

“…Moreover, a ''hedgerow'' arrangement of dimers was found in crystals of a c-domain derived from a Thermotoga maritima chemoreceptor; this arrangement is also suggested to have functional relevance (13). Finally, the size and diversity of the microbial chemoreceptor superfamily gives credence to the idea that the E. coli paradigm may not represent all of its members (7,16). The precise organization of receptors and signaling proteins is likely to be essential for function, but the full nature and role of the different arrangements are yet to be established.…”

“…The ligand-binding domains of the homologous chemoreceptors endow the array with responsiveness toward specific attractant molecules; the conserved cytoplasmic domain (c-domain) conveys signals generated by ligand binding. In addition, the sensitivities of receptors toward cognate ligands are adjusted by the reversible methylation of a few conserved glutamic acid residues in the c-domain (7). Temporal comparisons are made between current and recent past chemoeffector concentrations by pathway proteins that propagate and terminate signals, which serves to bias the random-walk swimming behavior of E. coli in chemical gradients (8).…”

Structural dynamics of protein lysine methylation and demethylation

“…Methylation can function as a reversible signal, as in the case of O(xygen)-methylation, in which the side chain carboxyl groups of glutamate residues or the C-terminal carboxyl groups are reversibly methylated [90,91]. There are many examples of N(itrogen)-methylations (of arginine, lysine, glutamine, asparagine, histidine residues, and the amino group at the N terminus) in the cell.…”