Identification of two genes, kpsM and kpsT, in region 3 of the polysialic acid gene cluster of Escherichia coli K1

Abstract

The polysialic acid capsule of Escherichia coli K1, a causative agent of neonatal septicemia and meningitis, is an essential virulence determinant. The 17-kb kps gene cluster, which is divided into three functionally distinct regions, encodes proteins necessary for polymer synthesis and expression at the cell surface. The central region, 2, encodes products required for synthesis, activation, and polymerization of sialic acid, while flanking regions, 1 and 3, are thought to be involved in polymer assembly and transport. In this study, we identified two genes in region 3, kpsM and kpsT, which encode proteins with predicted sizes of 29.6 and 24.9 kDa, respectively. The hydrophobicity profile of KpsM suggests that it is an integral membrane protein, while KpsT contains a consensus ATP-binding domain. KpsM and KpsT belong to a family of prokaryotic and eukaryotic proteins involved with a variety of biological processes, including membrane transport. A previously described kpsT chromosomal mutant that accumulates intracellular polysialic acid was characterized and could be complemented in trans. Results of site-directed mutagenesis of the putative ATP-binding domain of KpsT are consistent with the view that KpsT is a nucleotide-binding protein. KpsM and KpsT have significant similarity to BexB and BexA, two proteins that are essential for polysaccharide capsule expression in Haemophilus influenzae type b. We propose that KpsM and KpsT constitute a system for transport of polysialic acid across the cytoplasmic membrane.

NovelAeromonas hydrophilaPPD134/91 Genes Involved in O-Antigen and Capsule Biosynthesis

“…The ABC-2 of the E. coli group II capsule consists of KpsM (the transmembrane component) and KpsT (the ATPase component). KpsM has an ATP-binding fold and contains at least six potential membrane-spanning domains (41,55). It was speculated that the group II capsular polysaccharide transporter system comprises two molecules of KpsM to form some type of inner-membrane-spanning pore and two molecules of KpsT to catalyze ATP hydrolysis and energize the transport process.…”

A new subfamily of bacterial ABC‐type transport systems catalyzing export of drugs and carbohydrates

“…The consensus sequence is provided below the multiple alignment, and residues conserved in all five proteins are indicated by an exclamation mark above the multiple alignment. In addition to the DrrB protein of S. peucetius (Sp) (Guilfoile & Hutchinson, 1991), these proteins include the BexB protein of the polyribosylribitol phosphate capsular polysaccharide export system of Haemophilus influenzae (Hi) (Kroll et al, 1988, the CtrC protein of the polyneuraminic acid capsular polysaccharide export system of Neisseria meningitidi3 (Nm) (Frosch et al, 1991), the KpsM protein of the polyneuraminic acid capsular polysaccharide export system of Escherichia coli (Ec) (Smith et al, 1990;Pavelka et al, 1991), and the NodJ protein of R. leguminosarum (RI) (Evans & Downie, 1986). Table 1 summarizes the binary comparison scores (in standard deviations) for these five proteins.…”

Evidence that KpsT, the ATP-binding component of an ATP-binding cassette transporter, is exposed to the periplasm and associates with polymer during translocation of the polysialic acid capsule of Escherichia coli K1

“…This notion is based in part on the finding that wild-type cells overexpressing KpsT, despite being fully encapsulated, accumulate polymer in the cytoplasm (5). The observation that the genes encoding KpsM and KpsT overlap (16) suggests that these proteins are normally present in similar amounts to form transport complexes. Since increasing the amount of KpsT results in polymer accumulation, such accumulation may result from an interaction between these molecules as they await access to KpsM and translocation.…”

“…Translocation of polySia at the cytoplasmic membrane is mediated by an ATP-binding cassette (ABC) transporter, KpsMT, encoded by region 3 (16,17,21). ABC transporters have been described in organisms ranging in diversity from bacteria to humans and are involved in transport of a varied array of molecules in both directions across cell membranes (2,9).…”