title: Phosphotransfer site of the chemotaxis-specific protein kinase CheA as revealed by NMR.
abstract: Bacterial chemotaxis involves autophosphorylation of a histidine kinase and transfer of the phosphoryl group to response regulators to control flagellar rotation and receptor adaptation. The phosphotransfer domain, CheA1-134, of the chemotaxis-specific histidine autokinase CheA from Escherichia coli contains the site of phosphorylation, His48, and two other histidine residues, His26 and His67. Two-dimensional 1H-15N NMR techniques were applied to characterize the protonation states of these histidine residues and to evaluate the structural changes in the domain that occur upon phosphorylation of His48. The pKa of His48 was determined to be 7.8 (in 50 mM NaPO4 buffer at 30 degrees C). At high pH, its imidazole ring exists primarily as the normally unfavored N delta 1H tautomer, suggesting hydrogen bond formation to the ring nitrogen atom(s) to stabilize this state. The pKa values and predominant tautomeric states of the imidazole rings of His26 (pKa approximately 7.1, N epsilon 2H tautomer) and His67 (pKa approximately 6.5, N delta 1H tautomer) were also determined. His48 of CheA1-134 and CheA1-233 was phosphorylated by full-length CheA. The phosphorylation site was confirmed to be the N epsilon 2 position in the imidazole ring. Phosphorylation of His48 only results in small changes in the amide 1H and 15N chemical shifts of a few residues from helices B and C, suggesting that only very small changes in structure are associated with phosphorylation of the phosphotransfer domain of CheA. These residues occupy a small surface area of the helix bundle and form the active site of the protein. At the active site, in addition to His48, residues Gly52, His67, and Glu70 are conserved in the CheA homologous phosphotransfer domains from 10 different organisms. Sequence comparison of these CheA homologs suggest that the phosphotransfer domains likely fold in a similar helix-bundle structure and the structural features at the active site are well-conserved.
authors.affiliation: Institute of Molecular Biology, University of Oregon, Eugene 97403, USA.
authors.forename: H
authors.initials: H
authors.lastname: Zhou
authors.forename: F W
authors.initials: FW
authors.lastname: Dahlquist
mesh_terms: D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D002633:Chemotaxis / Q000502:physiology*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins; D006639:Histidine / Q000737:chemistry; D000071677:Histidine Kinase; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000072236:Methyl-Accepting Chemotaxis Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010766:Phosphorylation; D011487:Protein Conformation; D017510:Protein Folding; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D006639:Histidine; D011494:Protein Kinases; D000071677:Histidine Kinase; C000607608:cheA protein, E coli