Binding and accumulation of hemin in Neisseria gonorrhoeae

The ability to utilize hemin and hemin-containing compounds for nutritional iron (Fe) uptake has been documented for several pathogenic bacteria. Neisseria gonorrhoeae can utilize free hemin as a source of Fe for growth; however, little is known concerning the mechanisms involved in hemin transport. In this study we have characterized the binding and accumulation of hemin by N. gonorrhoeae and defined the specificity of the gonococcal hemin receptor. N. gonorrhoeae F62 was grown in a chemically defined medium containing the iron chelator Desferal, and hemin transport was initiated by the addition of [59Fe]hemin (4.0 or 8.0 microM; specific activity, 7.0 Ci/mol). 59Fe uptake from radiolabeled hemin by N. gonorrhoeae was energy dependent, and 59Fe was shown to accumulate in the cell at a constant rate during logarithmic growth. However, we observed a decrease in the uptake of 59Fe from radiolabeled hemin when inorganic iron was present in the growth medium. Binding of 59Fe from radiolabeled hemin was inhibited by the addition of either cold hemin, hematoporphyrin, or hemoglobin, but not by ferric citrate. Although [14C]hemin was found to support the growth of N. gonorrhoeae, we did not detect the uptake of 14C from radiolabeled hemin. Extraction of the gonococcal periplasmic ferric binding protein (Fbp) from cultures grown with [59Fe]hemin indicated that a majority of the 59Fe was associated with the Fbp. Taken together, the results presented here indicate that hemin binds to a gonococcal outer membrane receptor through the protoporphyrin portion of the molecule and that following binding, iron is removed and transported into the cell, where it is associated with the gonococcal periplasmic ferric binding protein, Fbp.