VlpA of Vibrio cholerae O1: the first bacterial member of the α2-microglobulin lipocalin superfamily

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Abstract
We have identified a gene,vlpA,which is closely linked to themfrA,Blocus associated with mannose-fucose-resistant haemagglutination. VlpA is an outer-membrane protein which can be labelled with [3H]palmitate and whose processing is globomycin-sensitive, suggesting that it is a lipoprotein. Homology searches revealed that VlpA belongs to the group of lipocalins of the α2-microglobulin superfamily which function as small hydrophobic molecule transporters, and is the first identified bacterial member of this group. Multiple copies of this gene are present inVibrio choleraeO1 and O139 and Southern hybridization reveals a biotype-specific pattern of fragment sizes. Construction of strains capable of hyperproducing VlpA suggested that it is able to bind haemin with low affinity but this may be due to a simple hydrophobic interaction. Attempts to construct specific mutants invlpAhave been unsuccessful, presumably because of the multiple copies ofvlpAgenes and their linkage to the VCR element.