TolB protein ofEscherichia coliK‐12 interacts with the outer membrane peptidoglycan‐associated proteins Pal, Lpp and OmpA

Abstract

SummaryThe Tol-Pal proteins of Escherichia coli are involved in maintaining outer membrane integrity. Transmembrane domains of TolQ, TolR and TolA interact in the cytoplasmic membrane, while TolB and Pal form a complex near the outer membrane. TolB and the central domain of TolA interact in vitro with the outer membrane porins. In this study, both genetic and biochemical analyses were carried out to analyse the links between TolB, Pal and other components of the cell envelope. It was shown that TolB could be cross-linked in vivo with Pal, OmpA and Lpp, while Pal was associated with TolB and OmpA. The isolation of pal and tolB mutants disrupting some interactions between these proteins represents a first approach to characterizing the residues contributing to the interactions. We propose that TolB and Pal are part of a multiprotein complex that links the peptidoglycan to the outer membrane. The Tol-Pal proteins might form transenvelope complexes that bring the two membranes into close proximity and help some outer membrane components to reach their final destination.

Dual orientation of the outer membrane lipoprotein Pal in Escherichia coli

“…Since its discovery in 1981 (Mizuno, 1981), Pal has been well studied (Godlewska et al, 2009); mostly notably for its interactions with other bacterial proteins (Bouveret et al, 1995;Cascales et al, 2000Cascales et al, , 2002Clavel et al, 1998), its proposed role in maintaining the integrity of the outer membrane of E. coli (Cascales et al, 2002) and its other physiological interaction with the peptidoglycan layer (Lazzaroni & Portalier, 1992). TolB and peptidoglycan compete for the same binding site on Pal, which happens to be on the opposite end (structurally) of the N-terminal lipid anchor (Abergel et al, 1999;Bouveret et al, 1995;Cascales & Lloubès, 2004;Parsons et al, 2006), thus making the interactions of Pal with TolB and peptidoglycan mutually exclusive.…”

“…For example, in the Tol-Pal complex, a combination of lipoproteins, integral membrane proteins and periplasmic proteins interact with each other and the peptidoglycan, forming a web of covalent and noncovalent contacts between the outer and inner membranes (Yeh et al, 2010). The outer membrane peptidoglycan associated lipoprotein (Pal; tethered to the outer membrane via its Nterminal lipid moiety) is one of the key components in the Tol-Pal complex (Godlewska et al, 2009;Gerding et al, 2007) interacting noncovalently with the peptidoglycan layer (Leduc et al, 1992;Bouveret et al, 1999), outer membrane proteins OmpA (Clavel et al, 1998) and Lpp (Cascales et al, 2002), periplasmic protein TolB (Bouveret et al, 1995 and the inner membrane protein TolA (Cascales et al, 2000;Deprez et al, 2005). Although the exact function of Pal is unknown, Pal deletion mutants in E. coli exhibit cell envelope defects and greater susceptibility to the antibiotic vancomycin (Bernadac et al, 1998;Cascales & Lloubès, 2004).…”

Depletion of Apolipoprotein N-Acyltransferase Causes Mislocalization of Outer Membrane Lipoproteins in Escherichia coli

“…(iv) ApoPal associates with the peptidoglycan or with outer membrane components such as OmpA (46), and its association with the plasma membrane is consequently disrupted when the cells are broken in the French press. Cross-linking of the plasma membrane apo-form of Lpp to the peptidoglycan could explain the cofractionation of the plasma and outer membrane pools from envelopes of Lnt Ec -depleted cells in sucrose gradients, because the peptidoglycan would be linked to both the outer membrane (via mature Lpp) and to the plasma membrane (via apoLpp).…”

Life Stage-specific Proteomes of Legionella pneumophila Reveal a Highly Differential Abundance of Virulence-associated Dot/Icm effectors

“…Furthermore, several known membrane proteins or some that are involved in the biogenesis of outer membrane proteins are among this group. These include the virulence factor and peptidyl-prolyl cis/trans isomerase Mip (76,77); Com1, another protein promoting bacterial pathogenicity and formation of stable disulfide-bond complexes, e.g. in Dot/Icm effectors (78,79); the periplasmic chaperone SurA, required for biogenesis of outer membrane proteins (80); DsbA, a disulfide oxidoreductase forming disulfide bonds when proteins emerge in the periplasm (81,82); LolA, an outer membrane lipoprotein carrier protein and part of the LolAB complex (83) which aids export of lipoproteins to the outer membrane in E. coli; and YjeA, a peptidoglycan deacetylase (84) (Fig.…”