Structure-function relationships in Escherichia coli adenylate cyclase.
Class I adenylate cyclases are found in gamma- and delta-proteobacteria. They play central roles in processes such as catabolite repression in Escherichia coli or development of full virulence in pathogens such as Yersinia enterocolitica and Vibrio vulnificus. The catalytic domain (residues 2-446) of the adenylate cyclase of E. coli was overexpressed and purified. It displayed a V(max) of 665 nmol of cAMP x mg(-1) x min(-1) and a K(m) of 270 microM. Titration of the metal cofactor Mg(2+) against the substrate ATP showed a requirement for free metal ions in addition to the MgATP complex, suggesting a two-metal-ion mechanism as is known for class II and class III adenylate cyclases. Twelve residues which are essential for catalysis were identified by mutagenesis of a total of 20 polar residues conserved in all class I adenylate cyclases. Five essential residues (Ser(103), Ser(113), Asp(114), Asp(116) and Trp(118)) were part of a region which is found in all members of the large DNA polymerase beta-like nucleotidyltransferase superfamily. Alignment of the E. coli adenylate cyclase with the crystal structure of a distant member of the superfamily, archaeal tRNA CCA-adding enzyme, suggested that Asp(114) and Asp(116) are the metal-cofactor-ion-binding residues. The S103A mutant had a 17-fold higher K(m) than wild-type, demonstrating its important role in substrate binding. In comparison with the tRNA CCA-adding enzyme, Ser(103) of the E. coli adenylate cyclase apparently binds the gamma-phosphate group of ATP. Consistent with this function, the S103A mutation caused a marked reduction of discrimination between ATP- and ADP- or AMP-derived inhibitors.
Linder
Jürgen U
JU
Department of Pharmacology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA. jul2015@med.cornell.edu
D000255:Adenosine Triphosphate / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011487:Protein Conformation; D012694:Serine / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
D029968:Escherichia coli Proteins; D012694:Serine; D000255:Adenosine Triphosphate; D000262:Adenylyl Cyclases