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Overproduction of Inactive Variants of the Murein Synthase PBP1B Causes Lysis in Escherichia coli

Ute Meisel, Joachim-Volker Höltje, and Waldemar Vollmer^*

Abteilung Biochemie, Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany

Received 20 March 2003/ Accepted 26 June 2003

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 (, ß, and ) 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.

Present address: Universität Tübingen, Fakultät für Biologie, Lehrbereich Mikrobielle Genetik, 72076 Tübingen, Germany.

Present address: Galerie Joho, Tübingen, 72072 Tübingen, Germany.

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