Evidence of a bactericidal permeability increasing protein in an invertebrate, theCrassostrea gigas Cg-BPI

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Abstract
A cDNA sequence with homologies to members of the LPS-binding protein and bactericidal/permeability-increasing protein (BPI) family was identified in the oysterCrassostrea gigas. The recombinant protein was found to bind LPS, to display bactericidal activity againstEscherichia coli, and to increase the permeability of the bacterial cytoplasmic membrane. This indicated that it is a BPI rather than an LPS-binding protein. Byin situhybridization, the expression of theC. gigasBPI (Cg-bpi) was found to be induced in hemocytes after oyster bacterial challenge and to be constitutive in various epithelia of unchallenged oysters. Thus,Cg-bpitranscripts were detected in the epithelial cells of tissues/organs in contact with the external environment (mantle, gills, digestive tract, digestive gland diverticula, and gonad follicles). Therefore,Cg-BPI, whose expression profile and biological properties are reminiscent of mammalian BPIs, may provide a first line of defense against potential bacterial invasion. To our knowledge, this is the first characterization of a BPI in an invertebrate.