| Primary Identifier | IPR020889 | Type | Family |
| Short Name | LipoPS_assembly_LptD |
| description | The cell envelope of Gram-negative bacteria consists of an inner (IM) and an outer membrane (OM) separated by an aqueous compartment, the periplasm, which contains the peptidoglycan layer. The OM is an asymmetric bilayer, with phospholipids in the inner leaflet and lipopolysaccharides (LPS) facing outward [, ]. The OM is an effective permeability barrier that protects the cells from toxic compounds, such as antibiotics and detergents, thus allowing bacteria to inhabit several different and often hostile environments. LPS is responsible for the permeability properties of the OM. LPS consists of the lipid A moiety (a glucosamine-based phospholipid) linked to the short core oligosaccharide and the distal O-antigen polysaccharide chain. The core oligosaccharide can be further divided into an inner core, composed of 3-deoxy-D-mannooctulosanate (KDO) and heptose, and an outer core, which has a somewhat variable structure. LPS is essential in most Gram-negative bacteria, with the notable exception of Neisseria meningitidis. The biogenesis of the OM implies that the individual components are transported from the site of synthesis to their final destination outside the IM by crossing both hydrophilic and hydrophobic compartments. The machinery and the energy source that drive this process are not yet fully understood. The lipid A-core moiety and the O-antigen repeat units are synthesized at the cytoplasmic face of the IM andare separately exported via two independent transport systems, namely, the O-antigen transporter Wzx (RfbX) [, ]and the ATP binding cassette (ABC) transporter MsbA that flips the lipid A-core moiety from the inner leaflet to the outer leaflet of the IM [, , ]. O-antigen repeat units are then polymerised in the periplasm by the Wzy polymerase and ligated to the lipid A-core moiety by the WaaL ligase [see, , ].The LPS transport machinery is composed of LptA, LptB, LptC, LptD, LptE. This supported by the fact, that depletion of any of one of these proteins blocks the LPS assembly pathway and results in very similar OM biogenesis defects. Moreover, the location of at least one of these five proteins in every cellular compartment suggests a model for how the LPS assembly pathway is organised and ordered in space [].LptD forms a complex with LptE, which is involved in the assembly of LPS in the outer leaflet of the outer membrane. It determines N-hexane tolerance and is involved in outer membrane permeability as well as being ssential for envelope biogenesis [, , ]. |
