Substrate binding by a bacterial ABC transporter involved in polysaccharide export

Journal Article · Wed Apr 02 04:00:00 EDT 2008 · Proc. Natl. Acad. Sci. USA

DOI:https://doi.org/10.1073/pnas.0705709104· OSTI ID:1007632

Cuthbertson, Leslie; Kimber, Matthew S; Whitfield, Chris ^[1]

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1. Guelph

ATP-binding-cassette (ABC) transporters are responsible for the export of a wide variety of cell-surface glycoconjugates in both Gram-positive and Gram-negative bacteria. These include the O-antigenic polysaccharide (O-PS) portion of lipopolysaccharide, a crucial virulence determinant in Gram-negative pathogens. O-PSs are synthesized by one of two fundamentally different pathways. Escherichia coli O serotypes O8 and O9a provide the prototype systems for studying O-PS export via ABC transporters. The transporter is composed of the transmembrane component Wzm and the nucleotide-binding component Wzt. Although the N-terminal domain of Wzt is a conventional ABC protein, the C-terminal domain of Wzt (C-Wzt) is a unique structural element that determines the specificity of the transporter for either the O8 or O9a O-PS. We show here that the two domains of Wzt can function when expressed as separate polypeptides; both are essential for export. In vitro, C-Wzt binds its cognate O-PS by recognizing a residue located at the nonreducing end of the polymer. The crystal structure of C-WztO9a is reported here and reveals a {beta} sandwich with an immunoglobulin-like topology that contains the O-PS-binding pocket. Substrate interactions with nucleotide-binding domains have been demonstrated in an ABC exporter previously. However, to our knowledge substrate binding by a discrete, cytoplasmic accessory domain in an extended nucleotide-binding domain polypeptide has not previously been demonstrated. Elucidation of the substrate-recognition system involved in O-PS export provides insight into the mechanism that coordinates polymer biosynthesis, termination, and export.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE
• OSTI ID: 1007632
• Journal Information: Proc. Natl. Acad. Sci. USA, Journal Name: Proc. Natl. Acad. Sci. USA Journal Issue: (49) ; 12, 2007 Vol. 104; ISSN PNASA6; ISSN 0027-8424
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
BACTERIA
BIOSYNTHESIS
CRYSTAL STRUCTURE
ESCHERICHIA COLI
EXPORTS
IN VITRO
PATHOGENS
POLYMERS
POLYPEPTIDES
POLYSACCHARIDES
RESIDUES
SPECIFICITY
SUBSTRATES
TOPOLOGY
VIRULENCE