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- Title
The catalytic, glycosyl transferase and acyl transferase modules of the cell wall peptidoglycan-polymerizing penicillin-binding protein 1b of Escherichia coli.
- Authors
Terrak, Mohammed; Ghosh, Tushar K; van Heijenoort, Jean; Van Beeumen, Jozef; Lampilas, Maxime; Aszodi, Jozsef; Ayala, Juan A; Ghuysen, Jean-Marie; Nguyen-Distèche, Martine
- Abstract
The penicillin-binding protein (PBP) 1b of Escherichia coli catalyses the assembly of lipid-transported N -acetyl glucosaminyl-β-1,4-N -acetylmuramoyl-l-alanyl-γ-d-glutamyl-(l)-meso -diaminopimelyl-(l)-d-alanyl-d-alanine disaccharide pentapeptide units into polymeric peptidoglycan. These units are phosphodiester linked, at C1 of muramic acid, to a C55 undecaprenyl carrier. PBP1b has been purified in the form of His tag (M46-N844) PBP1bγ. This derivative provides the host cell in which it is produced with a functional wall peptidoglycan. His tag (M46-N844) PBP1bγ possesses an amino-terminal hydrophobic segment, which serves as transmembrane spanner of the native PBP. This segment is linked, via an ≅ 100-amino-acid insert, to a D198-G435 glycosyl transferase module that possesses the five motifs characteristic of the PBPs of class A. In in vitro assays, the glycosyl transferase of the PBP catalyses the synthesis of linear glycan chains from the lipid carrier with an efficiency of ≅ 39 000 M-1 s-1 . Glu-233, of motif 1, is central to the catalysed reaction. It is proposed that the Glu-233 γ-COOH donates its proton to the oxygen atom of the scissile phosphoester bond of the lipid carrier, leading to the formation of an oxocarbonium cation, which then undergoes attack by the 4-OH group of a nucleophile N -acetylglucosamine. Asp-234 of motif 1 or Glu-290 of motif 3 could be involved in the stabilization of the oxocarbonium cation and the activation of the 4-OH group of the N -acetylglucosamine. In turn, Tyr-310 of motif 4 is an important component of the amino acid sequence-folding information. The glycosyl transferase module of PBP1b, the lysozymes and the lytic transglycosylase Slt70 have much the same catalytic machinery. They might be members of the same superfamily. The glycosyl transferase module is linked, via a short junction site, to the amino end of a Q447-N844 acyl transferase module, which...
- Subjects
ESCHERICHIA coli; CARRIER proteins; BACTERIAL cell walls; PEPTIDOGLYCANS
- Publication
Molecular Microbiology, 1999, Vol 34, Issue 2, p350
- ISSN
0950-382X
- Publication type
Article
- DOI
10.1046/j.1365-2958.1999.01612.x