The structure of Serratia marcescens Lip, a membrane-bound component of the type VI secretion system

Vincenzo A. Rao, Sharon M. Shepherd, Grant English, Sarah J. Coulthurst, William N. Hunter

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    Abstract

    Lip is a membrane-bound lipoprotein and a core component of the type VI secretion system found in Gram-negative bacteria. The structure of a Lip construct (residues 29-176) from Serratia marcescens (SmLip) has been determined at 1.92 angstrom resolution. Experimental phases were derived using a single-wavelength anomalous dispersion approach on a sample cocrystallized with iodide. The membrane localization of the native protein was confirmed. The structure is that of the globular domain lacking only the lipoprotein signal peptide and the lipidated N-terminus of the mature protein. The protein fold is dominated by an eight-stranded beta-sandwich and identifies SmLip as a new member of the transthyretin family of proteins. Transthyretin and the only other member of the family fold, 5-hydroxyisourate hydrolase, form homotetramers important for their function. The asymmetric unit of SmLip is a tetramer with 222 symmetry, but the assembly is distinct from that previously noted for the transthyretin protein family. However, structural comparisons and bacterial two-hybrid data suggest that the SmLip tetramer is not relevant to its role as a core component of the type VI secretion system, but rather reflects a propensity for SmLip to participate in protein-protein interactions. A relatively low level of sequence conservation amongst Lip homologues is noted and is restricted to parts of the structure that might be involved in interactions with physiological partners.

    Original languageEnglish
    Pages (from-to)1065-1072
    Number of pages8
    JournalActa Crystallographica Section D: Biological Crystallography
    Volume67
    DOIs
    Publication statusPublished - Dec 2011

    Keywords

    • BACTERIAL 2-HYBRID SYSTEM
    • RETINOL-BINDING-PROTEIN
    • 5-HYDROXYISOURATE HYDROLASE
    • CRYSTAL-STRUCTURES
    • ESCHERICHIA-COLI
    • OUTER-MEMBRANE
    • TRANSTHYRETIN
    • REFINEMENT
    • RECOGNITION
    • MECHANISM

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