Outer-membrane Lipoprotein LpoB Spans the Periplasm to Stimulate the Peptidoglycan Synthase PBP1B

Proc Natl Acad Sci U S A. 2014 Jun 3;111(22):8197-202. doi: 10.1073/pnas.1400376111. Epub 2014 May 12.

Abstract

Bacteria surround their cytoplasmic membrane with an essential, stress-bearing peptidoglycan (PG) layer. Growing and dividing cells expand their PG layer by using membrane-anchored PG synthases, which are guided by dynamic cytoskeletal elements. In Escherichia coli, growth of the mainly single-layered PG is also regulated by outer membrane-anchored lipoproteins. The lipoprotein LpoB is required for the activation of penicillin-binding protein (PBP) 1B, which is a major, bifunctional PG synthase with glycan chain polymerizing (glycosyltransferase) and peptide cross-linking (transpeptidase) activities. Here, we report the structure of LpoB, determined by NMR spectroscopy, showing an N-terminal, 54-aa-long flexible stretch followed by a globular domain with similarity to the N-terminal domain of the prevalent periplasmic protein TolB. We have identified the interaction interface between the globular domain of LpoB and the noncatalytic UvrB domain 2 homolog domain of PBP1B and modeled the complex. Amino acid exchanges within this interface weaken the PBP1B-LpoB interaction, decrease the PBP1B stimulation in vitro, and impair its function in vivo. On the contrary, the N-terminal flexible stretch of LpoB is required to stimulate PBP1B in vivo, but is dispensable in vitro. This supports a model in which LpoB spans the periplasm to interact with PBP1B and stimulate PG synthesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apolipoproteins B / chemistry
  • Apolipoproteins B / metabolism*
  • Bacterial Outer Membrane Proteins / chemistry
  • Bacterial Outer Membrane Proteins / metabolism*
  • Escherichia coli / enzymology*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Nuclear Magnetic Resonance, Biomolecular
  • Penicillin-Binding Proteins / chemistry
  • Penicillin-Binding Proteins / metabolism*
  • Peptidoglycan / biosynthesis
  • Peptidoglycan Glycosyltransferase / chemistry
  • Peptidoglycan Glycosyltransferase / metabolism*
  • Periplasm / metabolism
  • Protein Interaction Domains and Motifs
  • Protein Structure, Tertiary
  • Serine-Type D-Ala-D-Ala Carboxypeptidase / chemistry
  • Serine-Type D-Ala-D-Ala Carboxypeptidase / metabolism*

Substances

  • Apolipoproteins B
  • Bacterial Outer Membrane Proteins
  • Escherichia coli Proteins
  • Penicillin-Binding Proteins
  • Peptidoglycan
  • Peptidoglycan Glycosyltransferase
  • penicillin-binding protein 1B, E coli
  • Serine-Type D-Ala-D-Ala Carboxypeptidase

Associated data

  • PDB/2MII