title: Overproduction of inactive variants of the murein synthase PBP1B causes lysis in Escherichia coli.
abstract: Penicillin-binding protein 1B (PBP1B) of Escherichia coli is a bifunctional murein synthase containing both a transpeptidase domain and a transglycosylase domain. The protein is present in three forms (alpha, beta, and gamma) which differ in the length of their N-terminal cytoplasmic region. Expression plasmids allowing the production of native PBP1B or of PBP1B variants with an inactive transpeptidase or transglycosylase domain or both were constructed. The inactive domains contained a single amino acid exchange in an essential active-site residue. Overproduction of the inactive PBP1B variants, but not of the active proteins, caused lysis of wild-type cells. The cells became tolerant to lysis by inactive PBP1B at a pH of 5.0, which is similar to the known tolerance for penicillin-induced lysis under acid pH conditions. Lysis was also reduced in mutant strains lacking several murein hydrolases. In particular, a strain devoid of activity of all known lytic transglycosylases was virtually tolerant, indicating that mainly the lytic transglycosylases are responsible for the observed lysis effect. A possible structural interaction between PBP1B and murein hydrolases in vivo by the formation of a multienzyme complex is discussed.
authors.affiliation: Abteilung Biochemie, Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Meisel
authors.forename: Joachim-Volker
authors.initials: JV
authors.lastname: Höltje
authors.forename: Waldemar
authors.initials: W
authors.lastname: Vollmer
mesh_terms: D001426:Bacterial Proteins; D001433:Bacteriolysis / Q000502:physiology*; D002352:Carrier Proteins; D020134:Catalytic Domain; D002455:Cell Division / Q000502:physiology; D004789:Enzyme Activation; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins; D006602:Hexosyltransferases / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D002267:Muramoylpentapeptide Carboxypeptidase; D009154:Mutation; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics / Q000378:metabolism; D046915:Penicillin-Binding Proteins; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism*; D046928:Peptidoglycan Glycosyltransferase; D010458:Peptidyl Transferases / Q000235:genetics / Q000378:metabolism*; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D046915:Penicillin-Binding Proteins; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D046928:Peptidoglycan Glycosyltransferase; C478681:penicillin-binding protein 1B, E coli; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; D002267:Muramoylpentapeptide Carboxypeptidase; D009238:N-Acetylmuramoyl-L-alanine Amidase; D010453:Peptide Synthases; C021814:murein synthetase