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Identification of an ATP‐binding cassette transport system required for translocation of lipopolysaccharide O‐antigen side‐chains across the cytoplasmic membrane of Klebsiella pneumoniae serotype O1
Author(s) -
Bronner Dorothea,
Clarke Bradley R.,
Whitfield Chris
Publication year - 1994
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1994.tb02185.x
Subject(s) - biology , bacterial outer membrane , biochemistry , atp binding cassette transporter , plasmid , transmembrane protein , transmembrane domain , lipopolysaccharide , transport protein , gene cluster , membrane transport protein , membrane protein , escherichia coli , gene , transporter , membrane , receptor , endocrinology
Summary The rfb kpO1 gene cluster of Klebsiella pneumoniae O1 directs synthesis of the D‐galactan I component of the lipopolysaccharide O‐antigen. The first two genes in the rfb kpO1 cluster encode Rrfb kpO1 and RfbB KpO1 , with predicted sizes of 29.5 or 30.0 kDa and 27.4 kDa, respectively. RfbB KpO1 contains a consensus ATP‐binding domain and shares homology with several proteins which function as ATP‐binding components of cell surface polysaccharide transporters. RfbA KpO1 is predicted to be an integral membrane protein with five putative membrane‐spanning domains and its transmembrane topology was confirmed by Tn phoA mutagenesis. The hydropathy plot of RfbA KpO1 resembles KpsM, the transcytoplasmic membrane component of the capsular polysaccharide transporter from Escherichia coli K‐1 and K‐5. These relationships suggest that RfbA KpO1 and RfbB KpO1 belong to a family of two‐component ABC (ATP‐binding cassette) transporters. E. coli K‐12 containing a plasmid carrying an rfb KpO1 gene cluster deleted in rfbA KpO1 and rfbB KpO1 expresses rough lipopolysaccharide molecules on its surface and accumulates cytoplasmic O‐antigen. When RfbA KpO1 and RfbB KpO1 are supplied in trans by a compatible plasmid, O‐polysaccharide transport is restored and smooth D‐galactan l‐substituted lipopolysaccharide is produced. RfbA KpO1 and RfbB KpO1 are, therefore, proposed to constitute a system required for transport of D‐galactan I across the cytoplasmic membrane, where RfbA KpO1 represents the membrane‐spanning translocator and RfbB KpO1 couples the energy of ATP hydrolysis to the transport process.