MCP methyltransferase, CheR-type, SAM-binding domain, C-terminal (CheR_C)
Type: Domain

Methyl transfer from the ubiquitous S-adenosyl-L-methionine (AdoMet) to either nitrogen, oxygen or carbon atoms is frequently employed in diverse organisms ranging from bacteria to plants and mammals. The reaction is catalysed by methyltransferases (Mtases) and modifies DNA, RNA, proteins and small molecules, such as catechol for regulatory purposes. The various aspects of the role of DNA methylation in prokaryotic restriction-modification systems and in a number of cellular processes in eukaryotes including gene regulation and differentiation is well documented.

Three classes of DNA Mtases transfer the methyl group from AdoMet to the target base to form either N-6-methyladenine, or N-4-methylcytosine, or C-5-methylcytosine. In C-5-cytosine Mtases, ten conserved motifs are arranged in the same order . Motif I (a glycine-rich or closely related consensus sequence; FAGxGG in M.HhaI ), shared by other AdoMet-Mtases , is part of the cofactor binding site and motif IV (PCQ) is part of the catalytic site. In contrast, sequence comparison among N-6-adenine and N-4-cytosine Mtases indicated two of the conserved segments , although more conserved segments may be present. One of them corresponds to motif I in C-5-cytosine Mtases, and the other is named (D/N/S)PP(Y/F). Crystal structures are known for a number of Mtases . The cofactor binding sites are almost identical and the essential catalytic amino acids coincide. The comparable protein folding and the existence of equivalent amino acids in similar secondary and tertiary positions indicate that many (if not all) AdoMet-Mtases have a common catalytic domain structure. This permits tertiary structure prediction of other DNA, RNA, protein, and small-molecule AdoMet-Mtases from their amino acid sequences .

CheR proteins are part of the chemotaxis signaling mechanism in bacteria. Flagellated bacteria swim towards favourable chemicals and away from deleterious ones. Sensing of chemoeffector gradients involves chemotaxis receptors, transmembrane (TM) proteins that detect stimuli through their periplasmic domains and transduce the signals via their cytoplasmic domains . Signalling outputs from these receptors are influenced both by the binding of the chemoeffector ligand to their periplasmic domains and by methylation of specific glutamate residues on their cytoplasmic domains. Methylation is catalysed by CheR, an S-adenosylmethionine-dependent methyltransferase , which reversibly methylates specific glutamate residues within a coiled coil region, to form gamma-glutamyl methyl ester residues .

The structure of the Salmonella typhimurium chemotaxis receptor methyltransferase CheR, bound to S-adenosylhomocysteine, has been determined to a resolution of 2.0 A . The structure reveals CheR to be a two-domain protein, with a smaller N-terminal helical domain linked via a single polypeptide connection to a larger C-terminal α/β domain. The C-terminal domain has the characteristics of a nucleotide-binding fold, with an insertion of a small anti-parallel β-sheet subdomain. The S-adenosylhomocysteine-binding site is formed mainly by the large domain, with contributions from residues within the N-terminal domain and the linker region .

CheR proteins are part of the chemotaxis signaling mechanism which methylates the chemotaxis receptor at specific glutamate residues. This entry refers to the C-terminal SAM-binding domain of the CherR-type MCP methyltransferases, which are found in bacteria and archaea. This entry is found in association with

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