Avian air sac and plasma proteins that bind surface polysaccharides of Escherichia coli O2

Some serovars of Escherichia coli, mainly O2 and O78, are responsible for air sac and systemic infections in farm-raised turkeys (Meleagris gallopavo) and chickens (Gallus gallus). We looked in air sac surface fluid from young turkeys to identify proteins that bind surface polysaccharides of pathogenic respiratory E. coli O2. Turkey air sac surface fluid was subjected to affinity chromatography on Toyopearl AF-Epoxy-650M, coupled with either lipopolysaccharide (LPS) or lipid-free polysaccharide (LFP) purified from an avian pathogenic E. coli O2 isolate. A multimeric protein termed lipid-free polysaccharide binding protein-40 (LFPBP-40) composed of six covalently associated subunits of approximately 40 kDa was isolated by elution from LFP by EDTA or L-rhamnose. An analogous protein in air sac fluid proteins bound to intact E. coli O2 and eluted with L-rhamnose or N-acetylglucosamine (GlcNAc). The N-terminal amino acid sequence of LFPBP-40 DINGGGATLPQHLYLTPDV was related to the N-terminus of fragment 3 of a partially characterized human protein possessing T cell stimulation activity in synovial membrane of rheumatoid arthritis patients. However, endogenous amino acid sequences were unrelated to other known proteins. LFPBP-40 was immunoreactively distinct from pulmonary collectins and ficolins. These studies demonstrate a novel avian respiratory soluble lectin that can bind surface polysaccharides of pathogenic E. coli responsible for respiratory disease.