title: Structure of a slow processing precursor penicillin acylase from Escherichia coli reveals the linker peptide blocking the active-site cleft.
abstract: Penicillin G acylase is a periplasmic protein, cytoplasmically expressed as a precursor polypeptide comprising a signal sequence, the A and B chains of the mature enzyme (209 and 557 residues respectively) joined by a spacer peptide of 54 amino acid residues. The wild-type AB heterodimer is produced by proteolytic removal of this spacer in the periplasm. The first step in processing is believed to be autocatalytic hydrolysis of the peptide bond between the C-terminal residue of the spacer and the active-site serine residue at the N terminus of the B chain. We have determined the crystal structure of a slowly processing precursor mutant (Thr263Gly) of penicillin G acylase from Escherichia coli, which reveals that the spacer peptide blocks the entrance to the active-site cleft consistent with an autocatalytic mechanism of maturation. In this mutant precursor there is, however, an unexpected cleavage at a site four residues from the active-site serine residue. Analyses of the stereochemistry of the 260-261 bond seen to be cleaved in this precursor structure and of the 263-264 peptide bond have suggested factors that may govern the autocatalytic mechanism.
authors.affiliation: Department of Chemistry, University of York, Heslington York, YO10 5DD, UK.
authors.forename: L
authors.initials: L
authors.lastname: Hewitt
authors.forename: V
authors.initials: V
authors.lastname: Kasche
authors.forename: K
authors.initials: K
authors.lastname: Lummer
authors.forename: R J
authors.initials: RJ
authors.lastname: Lewis
authors.forename: G N
authors.initials: GN
authors.lastname: Murshudov
authors.forename: C S
authors.initials: CS
authors.lastname: Verma
authors.forename: G G
authors.initials: GG
authors.lastname: Dodson
authors.forename: K S
authors.initials: KS
authors.lastname: Wilson
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004583:Electrons; D004792:Enzyme Precursors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D006860:Hydrogen Bonding; D006867:Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D005810:Multigene Family; D009154:Mutation / Q000235:genetics; D010399:Penicillin Amidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals; D012694:Serine / Q000737:chemistry / Q000378:metabolism
chemical_list: D004792:Enzyme Precursors; D010446:Peptide Fragments; D021382:Protein Sorting Signals; D012694:Serine; D006867:Hydrolases; D010399:Penicillin Amidase