Identification and purification of a conserved heme-regulated hemoglobin-binding outer membrane protein from Haemophilus ducreyi.

A hemoglobin-binding protein (HgbA) from Haemophilus ducreyi was identified and purified. The 100-kDa HgbA was detected in all strains of H. ducreyi tested, and a somewhat larger hemoglobin-binding protein was found in one strain of Haemophilus influenzae. HgbA was purified and the amino acid sequence of the N terminus of HgbA revealed no significant homologies with known proteins. Two different antisera to HgbA from H. ducreyi 35000 recognized HgbA proteins from all tested H. ducreyi strains; they did not recognize proteins from the H. influenzae strain. Expression of HgbA was regulated by the level of heme but not by iron present in the medium. Animal species of hemoglobin competed with iodinated human hemoglobin for binding to whole cells of H. ducreyi and supported the growth of H. ducreyi. The lack of immunological cross-reactivity and the differences in hemoglobin specificities between the H. ducreyi and the H. influenzae hemoglobin-binding proteins suggest that they are unrelated.