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Acta Crystallogr D Biol Crystallogr. 2011 Dec;67(Pt 12):1065-72. doi: 10.1107/S0907444911046300. Epub 2011 Nov 18.

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

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  • 1College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland.

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 Å 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 β-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.

PMID:
22120744
PMCID:
PMC3225178
DOI:
10.1107/S0907444911046300
[PubMed - indexed for MEDLINE]
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