title: Crystal structure of pentapeptide-independent chemotaxis receptor methyltransferase (CheR) reveals idiosyncratic structural determinants for receptor recognition.
abstract: Chemotactic methyltransferase, CheR catalyse methylation of specific glutamate residues in the cytoplasmic domain of methyl-accepting chemotactic protein receptors (MCPRs). The methylation of MCPRs is essential for the chemical sensing and chemotactic bacterial mobility towards favorable chemicals or away from unfavorable ones. In this study, crystal structure of B. subtilis CheR (BsCheR) in complex with S-adenosyl-l-homocysteine (SAH) has been determined to 1.8Å resolution. This is the first report of crystal structure belonging to the pentapeptide-independent CheR (PICheR) class. Till date, only one crystal structure of CheR from S. typhimurium (StCheR) belonging to pentapeptide-dependent CheR (PDCheR) class is available. Structural analysis of BsCheR reveals a helix-X-helix motif (HXH) with Asp53 as the linker residue in the N-terminal domain. The key structural features of the PDCheR β-subdomain involved in the formation of a tight complex with the pentapeptide binding motif in MCPRs were found to be absent in the structure of BsCheR. Additionally, isothermal titration calorimetry (ITC) experiments were performed to investigate S-adenosyl-(l)-methionine (SAM) binding affinity and KDwas determined to be 0.32mM. The structure of BsCheR reveals that mostly residues of the large C-terminal domain contribute to SAH binding, with contributions of few residues from the linker region and the N-terminal domain. Structural investigations and sequence analysis carried out in this study provide critical insights into the distinct receptor recognition mechanism of the PDCheR and PICheR methyltransferase classes.
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India.
authors.forename: Monu
authors.initials: M
authors.lastname: Batra
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Sharma
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India.
authors.forename: Anjali
authors.initials: A
authors.lastname: Malik
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India.
authors.forename: Sonali
authors.initials: S
authors.lastname: Dhindwal
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India.
authors.forename: Pravindra
authors.initials: P
authors.lastname: Kumar
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India. Electronic address: shailfbt@iitr.ac.in.
authors.forename: Shailly
authors.initials: S
authors.lastname: Tomar
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D002633:Chemotaxis; D000072236:Methyl-Accepting Chemotaxis Proteins / Q000737:chemistry*; D008780:Methyltransferases / Q000737:chemistry*; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D044042:Receptors, Formyl Peptide / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D010455:Peptides; D044042:Receptors, Formyl Peptide; D008780:Methyltransferases
keywords: Chemotaxis; Isothermal titration calorimetry; Methylation; Methyltransferase