Pal Lipoprotein ofEscherichia coliPlays a Major Role in Outer Membrane Integrity

Abstract

The Tol-Pal system of gram-negative bacteria is composed of five proteins. TolA, TolQ, and TolR are inner membrane proteins, TolB is a periplasmic protein, and Pal, the peptidoglycan-associated lipoprotein, is anchored to the outer membrane. In this study, the roles of Pal and major lipoprotein Lpp were compared in Escherichia coli. lpp and tol-pal mutations have previously been found to perturb the outer membrane permeability barrier and to cause the release of periplasmic proteins and the formation of outer membrane vesicles. In this study, we showed that the overproduction of Pal is able to restore the outer membrane integrity of an lpp strain but that overproduced Lpp has no effect in a pal strain. Together with the previously reported observation that overproduced TolA complements an lpp but not a pal strain, these results indicate that the cell envelope integrity is efficiently stabilized by an epistatic Tol-Pal system linking inner and outer membranes. The density of Pal was measured and found to be lower than that of Lpp. However, Pal was present in larger amounts compared to TolA and TolR proteins. The oligomeric state of Pal was determined and a new interaction between Pal and Lpp was demonstrated.

Differential Binding of Escherichia coli O157:H7 to Alfalfa, Human Epithelial Cells, and Plastic Is Mediated by a Variety of Surface Structures

“…Another possibility is that TdcA controls the expression of other adhesins in E. coli O157:H7 but that their functions or location in the outer membrane is impaired by ompA mutation. This hypothesis is supported by previous data indicating that the C-terminal end of OmpA displays binding to peptidoglycan (13) and to the Pal protein (in the Tol-Pal system), which has a critical role in outer membrane integrity (7). Studies in progress will determine more precisely the change in OmpA expression and the specific role played by this protein during the adhesion of E. coli O157:H7 to abiotic, plant, and animal surfaces.…”

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.…”

“…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). Pal has also been shown to dimerize in the presence of Lpp and OmpA (Cascales et al, 2002), although the physiological significance of dimerization is unknown.…”

“…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).…”

Peptidoglycan-associated lipoprotein ofAggregatibacter actinomycetemcomitansinduces apoptosis and production of proinflammatory cytokines via TLR2 in murine macrophages RAW 264.7in vitro

“…It is an important member of the TOL-PAL family which is involved in maintaining the cell wall organization [20], but it also functions as a pro-inflammatory agent in Gram-negative infections. For example, Escherichia coli PAL is released into the bloodstream and has a pathogenic role in Gram-negative sepsis in a mouse model [21], and a form of E. coli PAL which is released into human serum in vitro is able to induce pro-inflammatory cytokine production by mouse macrophages [22].…”