AFA‐I, a cloned afimbrial X‐type adhesin from a human pyelonephritic Escherichia coli strain: Purification and chemical, functional and serlologic characterization

Abstract

AFA‐I, a mannise‐resistant, p‐independent, X‐binding afimbrial Escherichia coli adhesin was purified from a recombinant strain and chemically, functionally and serologically characterized. AFA‐I exists on the bacterial surface and free as a macromolecular aggregate in the supernatant of spent culture medium. It is composed of a single, repeating 16‐kDa polypeptide subunit. The AFA‐I protein amino acid composition is remarkable for the presence of 22% non‐polar hydrophobic residues and 2.5 – 3.0 cysteines per subunit. Since AFA‐I travels as a monomer in sodium dodecyl sulfate/polyacrylamide gel electrophoresis under non‐reducing condition, no disulfide bonds exist between subunits and at least one free sulfhydryl per subunit is available. The AFA‐I N‐terminal amino acid sequence residues 1 – 24 was unrelated to E. coli fimbrial sequences; however, the N‐terminus of AFA‐I and GV‐12, another E. Coli afimbrial protein, was asparagine. HB101 (pIL 14), the AFA‐I recombinant strain, agglutinated only human and gorilla erythrocytes, indicating a preference for receptor molicules on the red cells of man and the anthropoid apes. AFA‐I did not bind glycophorin A or Sialyl glycosides and is therefore distinct from the E. coli X‐binding adhesins with M and S specificity. The AFA‐I receptor was found to be abundant and diffusely distributed on HeLa tissue culture monolayer cel surfaces by indirect fluorescent microscopy. Anti‐AFA‐I sera bound AFA‐I in Western blots of 4 out 16 X‐binding E. coli urine isolates. They did not bind MS or P pili. AFA‐I may be exemplary of an adhesin class significant for the pathogenesis of human urinary tract infection. Copyright © 1985, Wiley Blackwell. All rights reserved