Characterization of Porcine AIDA-I Adhesin and Its Receptors

by Fang, Yuanmu

A relatively high percentage of porcine Escherichia coli isolates from cases associated with neonatal and post-weaning diarrhea are positive for the gene encoding the adhesin involved in diffuse adherence I (AIDA-I). This gene and its corresponding protein were first identified and characterized in E. coli strain 2787 isolated from human infantile diarrhea. Little is known about the role of the AIDA-I protein in pathogenesis of porcine enteric disease caused by AIDA-I positive E. coli and the properties of AIDA-I protein expressed by porcine AIDA-I positive E. coli isolates and its receptors.

In this study, we demonstrated that AIDA-I adhesin isolated from porcine AIDA-I positive E. coli PD20 and PD58 is an acidic protein consisting of five isoforms. It has a molecular weight (100 kDa) similar to the AIDA-I adhesin expressed by human AIDA-I positive E. coli strain 2787 and has a relatively high amino acid homology (78-87%) with it. Immunodetection of AIDA-I positive E. coli strains using polyclonal anti-AIDA-I antibodies had relatively low sensitivity and specificity, accordingly these tests are unlikely to be used for regular diagnostic detection.

Using affinity chromatography, we isolated from porcine intestinal mucus proteins that bind to purified AIDA-I adhesin. These proteins were separated by one- and two-dimensional electrophoresis and subjected to overlay Western blot with purified AIDA-I adhesin and AIDA-I positive E. coli to demonstrate 65 and 120 kDa (p65 and p120) proteins as AIDA-I binding proteins. The identity of p65 was not determined based on LCMS/MS data, whereas p120 was matched to two nuclear proteins (namely, DNA damage binding protein and splicing factor 3b) and one cytoplasmic protein, which is an IgG Fc binding protein. Based on similar amino acid homology, molecular weight, structural similarity to mucin and reported evidence of being secreted by goblet cells into the intestinal lumen, we think that the IgG Fc binding protein is the most likely candidate to serve as a potential receptor in intestinal mucus for AIDA-I adhesin.