Purification and characterization of a family of high molecular weight surface-array proteins from Campylobacter fetus

Abstract

A variety of Gram-negative and Gram-positive bacteria possess crystalline surface layers, although little is known of their function. We previously have shown that the high molecular weight surface-array proteins of Campylobacter fetus are important in both the pathogenicity and antigenicity of this organism. For biochemical and immunological characterization, we purified high molecular weight (100,000, 127,000, 149,000) surface-array proteins from three C. fetus strains using sequential gel filtration and ion exchange high performance liquid chromatography. These proteins are acidic with pI values between 4.12 and 4.25 and contain large proportions of acidic amino acids (19.7%-22.0%) in addition to hydrophobic amino acids (37.3%-38.5%). They share a novel amino-terminal sequence through at least 19 residues. Carbohydrate analysis using periodic acid-Schiff staining and treatment with trifluoromethanesulfonic acid shows no evidence of glycosylation. Antiserum to a purified Mr = 100,000 protein from C. fetus 82-40 LP cross-reacts with three other purified C. fetus surface-array proteins by enzyme-linked immunosorbent assay with titers greater than 12,800. We conclude that: 1) there is a family of surface-array proteins of C. fetus with common structural and antigenic characteristics; 2) that these molecules have similar biochemical characteristics to surface-array proteins described for other bacteria; but however, 3) by amino-terminal sequence analysis these are unique.