Notes For:
Lipopolysaccharide (LPS), which is a major component of the outer leaflet of the outer membranes of Gram-negative bacteria, consists of lipid A linked to a short core oligosaccharide (lipid A-core) plus a distal O-antigen polysaccharide chain (which is absent in E. coli K-12). MsbA, a member of the ATP Binding Cassette (ABC) Superfamily of transporters, is essential for the translocation of lipid A-core from the inner leaflet to the outer leaflet of the inner membrane.
MsbA is an inner membrane protein; it consists of an N-terminal membrane spanning domain and a C-terminal nucleotide binding domain |CITS: [8094880][8809774]|. MsbA binds ATP |CITS: [8809774]|. MsbA is a homodimer; the MsbA monomer consists of an integral membrane domain containing 6 transmembrane alpha-helices and a cytoplasmic nucleotide binding domain |CITS: [18024585]|. Structures of MsbA (from K-12 or serotype O157:H7) in the inward facing, nucleotide free state with and without LPS bound |CITS: [18024585][28869968]|, of ADP-bound MsbA and of vanadate trapped MsbA |CITS: [28869968]| have been reported. MsbA may conform to an alternating access model of transport; conformational changes during the transport cycle have been widely investigated (see |CITS: [15222771][15807544][17029409][15890883][17927448][19278995][19996093][20715055][23766512][23306205][28869968][31899087]|.
Proteoliposomes prepared from purifed MsbA and phospholipids have an intrinsic ATPase activity which is further stimulated by the addition of hexa-acylated Kdo2-lipid A or hexa-acylated lipid A (but not by Lipid A precursors) |CITS: [12119303]|. LPS transport to the outer membrane in spheroplasts is dependent on the presence of MsbA |CITS: [15576375]|. MsbA does not function as a phospholipid flippase |CITS: [12714595]|. Purified, solubilised MsbA is homodimeric and its ATPase activity is stimulated by lipid A; the ATPase activity of MsbA reconstituted in proteoliposomes is inhibited by the phosphate analog, vanadate |CITS: [18344567]|. Purified MsbA, reconstituted in proteoliposomes, functions as an ATP dependent lipid flippase |CITS: [20412049]|. MsbA does not transport underacylated lipid A (tetra-acylated and penta-acylated Lipid A) as efficiently as hexa-acylated Lipid A |CITS: [9575204][33833055]|.
Overexpression of msbA suppresses the lethality of |FRAME: EG10464 lpxL| null mutants by increasing the translocation of LPS or its precursor, N-acetyl glucosamine, to the outer membrane; depletion of MsbA results in increased retention of labelled N-acetyl glucosamine in the inner membrane |CITS: [8809774]|. Overexpression of msbA relieves accumulation of tetra-acylated lipid A and glycerophospholipids in the inner membrane to allow growth of lpxL null mutants |CITS: [9575204]|. Depletion of MsbA results in the the accumulation of hexa-acylated lipid A species and glycerophospholipids within the inner membrane |CITS: [9575204]|. The transport of lipids (both lipopolysaccharide and phospholipid) to the outer membrane is blocked in an MsbA(A270T) temperature sensitive mutant grown at the non-permissive temperature |CITS: [11278265]|. Single amino acid substitutions in MsbA [MsbA(P18S) or MsbA(P50S)] or overexpression of msbA suppresses an otherwise lethal |FRAME: KDO Kdo| deletion phenotype |CITS: [17163638][18093093]| (see also |CITS: [34065855]|).
Cardiolipin impacts transport of LPS across the inner membrane; overexpression of msbA suppresses the lethality of a Δ|FRAME: EG11608 clsA| Δ|FRAME: EG10614 lpxM| double mutant |CITS: [33833055]|.
MsbA has sequence similarity with the human multidrug resistance protein, Mdr1 |CITS: [8094880]|. Purified MsbA, reconstituted in proteoliposomes, mediates the transport of the DNA dye, Hoechst 33342; MsbA ATPase activity is stimulated by Hoechst 33342 and by the cytotoxic drugs, vinblastine and daunomycin |CITS: [12842882]|. MsbA expressed in the gr...
| Reference(s): |
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