Isolation, characterization, and antimicrobial properties of bovine oligosaccharide-binding protein - A microbicidal granule protein of eosinophils and neutrophils

Peptidoglycan recognition proteins (PGRPs) constitute a recently characterized family of pattern-recognition molecules that are conserved from insects to humans and are implicated in mammalian innate immunity. Here we report the isolation, characterization, cDNA cloning, and antimicrobial activities of a bovine PGRP ortholog termed bovine oligosaccharide-binding protein (bOBP). Milligram quantities of bOBP were purified from peripheral leukocytes, thus allowing for the characterization of the disulfide array and for determining the in vitro antimicrobial activities of the native protein. Of the tissues analyzed, bOBP mRNA was detected only in bone marrow where the protein is synthesized as a 190 amino acid precursor. The mature 169 amino acid protein is stored in the cytoplasmic granules of neutrophils and eosinophils but is absent from lymphocytes, monocytes, and platelets. bOBP was microbicidal for Gram-positive and Gram-negative bacteria and yeast at low micromolar concentrations. The finding that bOBP was microbicidal for organisms in which peptidoglycan is absent (Cryptococcus neoformans) or buried (Salmonella typhimurium) indicates that previous conclusions about the specificity of peptidoglycan recognition proteins must be reevaluated and suggests that other envelope components may mediate the antimicrobial action of PGRP family members.