title: Crystal structure of PBP2x from a highly penicillin-resistant Streptococcus pneumoniae clinical isolate: a mosaic framework containing 83 mutations.
abstract: Penicillin-binding proteins (PBPs) are the main targets for beta-lactam antibiotics, such as penicillins and cephalosporins, in a wide range of bacterial species. In some Gram-positive strains, the surge of resistance to treatment with beta-lactams is primarily the result of the proliferation of mosaic PBP-encoding genes, which encode novel proteins by recombination. PBP2x is a primary resistance determinant in Streptococcus pneumoniae, and its modification is an essential step in the development of high level beta-lactam resistance. To understand such a resistance mechanism at an atomic level, we have solved the x-ray crystal structure of PBP2x from a highly penicillin-resistant clinical isolate of S. pneumoniae, Sp328, which harbors 83 mutations in the soluble region. In the proximity of the Sp328 PBP2x* active site, the Thr(338) --> Ala mutation weakens the local hydrogen bonding network, thus abrogating the stabilization of a crucial buried water molecule. In addition, the Ser(389) --> Leu and Asn(514) --> His mutations produce a destabilizing effect that generates an "open" active site. It has been suggested that peptidoglycan substrates for beta-lactam-resistant PBPs contain a large amount of abnormal, branched peptides, whereas sensitive strains tend to catalyze cross-linking of linear forms. Thus, in vivo, an "open" active site could facilitate the recognition of distinct, branched physiological substrates.
authors.affiliation: Laboratoire de Cristallographie Macromoléculaire, Institut de Biologie Structurale Jean-Pierre Ebel (CNRS/Commissariat à l'Energie Atomique), 41, rue Jules Horowitz, 38027 Grenoble, France. dessen@ibs.fr
authors.forename: A
authors.initials: A
authors.lastname: Dessen
authors.forename: N
authors.initials: N
authors.lastname: Mouz
authors.forename: E
authors.initials: E
authors.lastname: Gordon
authors.forename: J
authors.initials: J
authors.lastname: Hopkins
authors.forename: O
authors.initials: O
authors.lastname: Dideberg
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001216:Asparagine / Q000737:chemistry; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D004351:Drug Resistance; D007930:Leucine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D013296:Streptococcus pneumoniae / Q000737:chemistry*; D013912:Threonine / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D046915:Penicillin-Binding Proteins; D010406:Penicillins; C072223:PBP 2x protein, Streptococcus; D013912:Threonine; D001216:Asparagine; D007930:Leucine; D000409:Alanine