TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
*1.B.42.1.1









LPS-export porin (organic solvent tolerance protein, OstA)
Bacteria
Proteobacteria
OstA of Neisseria meningitidis (NP_273336)
*1.B.42.1.2









LPS export porin complex, LptBCFG-A-DE, consists of LptD (Omp; OmpA; 784 aas)-LptE (RlpB; 193 aas; O.M. lipoprotein)-LptA (KdsD; YhbN; OstA small; 185 aas periplasmic chaparone protein)-LptB (KdsC; YhbG; 241 aas cytoplasmic ABC-type ATPase)-LptC (YrbK, 199aas;1 N-terminal TMS)- LptFG, part of the ABC transporter. LptDE (1:1 stoichiometry) comprise a two-protein β-barrel-lipoprotein complex in the outer membrane that assembles and exports LPS (Chng et al., 2010).  After LPS (or a precursor) is transported across the inner membrane by MsbA (3.A.1.106.1), this seven component system translocates LPS from the outer surface of the inner membrane to the outer surface of the outer membrane using ATP hydrolysis to sequentially energize transfer from one binding site to another in several steps (Freinkman et al. 2012; Okuda et al. 2012; Sherman et al. 2014).  LPS interacts with LptC and LptA sequentially before being passed to the LptD outer membrane porin, anchored by the LptE lipoprotein on the inner surface of the outer membrane.  LptF and LptG are the transmembrane consituents of the ABC pump, and LptB is the ATPase of an ABC-like system that energizes the transport using several ATP molecules (Okuda et al. 2012; Sherman et al. 2014).  LptC interconnects the LptBFG ABC system with the periplasmic LptA protein via its large periplasmic domain (Villa et al. 2013).  LptDE form a complex in the outer membrane which inserts LPS into this membrane.  The 3-D strcture of the complex shows that the LptE lipoprotein inserts into the 26 stranded barrel of LptD as a plug.  The first two strands of LptD contain prolines and are therefore distorted, possibly creating a portal for lateral diffusion of LPS into the outer leaflet of the outer membrane (Qiao et al. 2014).  The 3-d structure of the Pseudomonas aeruginosa LptA, LptH, has been solved at 2:75 Å resolution revealing a β-jellyroll fold similar to that in LptD (Bollati et al. 2015). Direct interaction of LptB and LptC has been demonstrated (Martorana et al. 2016). A specific binding site in the LptB ATPase for the coupling helices of the transmembrane LptFG complex is responsible for coupling ATP hydrolysis by LptB with LptFG function to achieve LPS extraction (Simpson et al. 2016). After biosynthesis, bacterial lipopolysaccharides (LPS) are transiently anchored to the outer leaflet of the inner membrane (IM). The ABC transporter LptB2FG extracts LPSs from the IM and transports them to the outer membrane. Luo et al. 2017 reported the crystal structure of nucleotide-free LptB2FG from P. aeruginosa. It shows that LPS transport proteins LptF and LptG each contain a TM domain (TMD), a periplasmic beta-jellyroll-like domain and a coupling helix that interacts with LptB on the cytoplasmic side. The LptF and LptG TMDs form a large outward-facing V-shaped cavity in the IM. Mutational analyses suggested that LPS may enter the central cavity laterally, via the interface of the TMD domains of LptF and LptG, and is expelled into the beta-jellyroll-like domains upon ATP binding and hydrolysis by LptB. These studies suggest a mechanism for LPS extraction by LptB2FG that is distinct from those of classical ABC transporters that transport substrates across the IM (Luo et al. 2017).

Bacteria
Proteobacteria
LptA-G of E. coli:
LptA (YhbN; OstA(s)) (P0ADV1)
LptB (YhbG; ATPase) (P0A9V1)
LptC (YrbG) (P0ADW0)
LptD (OstA; Imp) (P31554)
LptE (RlpB) (P0ADC1)
LptF (YjgP) (P0AF98)
LptG (YjgQ) (P0ADC6)
*1.B.42.1.3









OstA homologue (Bhat et al. 2011).

Bacteria
Proteobacteria
OstA homologue of Myxococcus xanthus
*1.B.42.1.4









OstA of 842 aas

Bacteria
Proteobacteria
OstA of Rhodopseudomonas palustris
*1.B.42.1.5









OstA of 753 aas

Bacteria
Proteobacteria
OstA of Helicobacter pylori
*1.B.42.1.6









OstA 0f 680 aas

Bacteria
Aquificae
OstA of Hydrogenobaculum sp.
*1.B.42.1.7









OstA of 880 aas

Bacteria
Bacteroidetes/Chlorobi group
OstA of Chlorobium luteolum
*1.B.42.1.8









OstA of 894 aas

Bacteria
Bacteroidetes/Chlorobi group
OstA of Nonlabens dokdonensis
*1.B.42.1.9









OstA of 833 aas

Bacteria
Chlamydiae/Verrucomicrobia group
OstA of Methylacidiphilum infernorum
*1.B.42.1.10









OstA homologue of 991 aas

Bacteria
Spirochaetes
OstA homologue of Leptospira interrogans
*1.B.42.1.11









OstA of 975 aas

Bacteria
Spirochaetes
OstA of Brachyspira hyodysenteriae
*1.B.42.1.12









OstA of 537 aas

Bacteria
Firmicutes
OstA of Halobacteroides halobius
*1.B.42.1.13









Putative LptF-LptG-LptD (OstA) fusion protein of 1040 aas (may be an artifact due to a sequencing error, and may also be a contaminant, accounting for its occurance in a Firmicute.

Bacteria
Firmicutes
OstA of Halothermothrix orenii
*1.B.42.2.1









OstA homologue of 1069 aa

Bacteria
Spirochaetes
OstA of Treponema denticola