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

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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.

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