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Publication Abstract from PubMed

Many human dwelling bacteria acquire sialic acid for growth or surface display. We previously identified a sialic acid utilisation operon in Tannerella forsythia that includes a novel outer membrane sialic acid transport system (NanOU) where NanO is a putative TonB-dependent receptor and NanU a predicted SusD family protein. Using heterologous complementation of nanOU genes into an Escherichia coli strain devoid of outer membrane sialic acid permeases, we show that the nanOU system from the gut bacterium Bacteroides fragilis is functional and demonstrate its dependence on TonB for function. We also show that nanU is required for maximal function of the transport system, is expressed in a sialic acid responsive manner and determine its cellular localisation to the outer membrane using fractionation and immunofluorescence experiments. Ligand binding studies revealed high-affinity binding of sialic acid to NanU (Kd ~400 nM) from two Bacteroidetes species as well as binding of a range of sialic acid analogues. Determination of the crystal structure of NanU revealed a monomeric SusD-like structure containing a novel motif characterised by an extended kinked helix that might determine sugar-binding specificity. These data characterise the first bacterial extracellular sialic acid binding protein and define a sialic acid-specific Polysaccharide Utilisation Locus (PUL).

Structural and functional characterisation of NanU, a novel high-affinity sialic acid-inducible binding protein of oral and gut-dwelling Bacteroidetes spp.,Phansopa C, Roy S, Rafferty JB, Douglas CW, Pandhal J, Wright PC, Kelly DJ, Stafford GP Biochem J. 2013 Dec 19. PMID:24351045^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.