RIFTIA HEMOGLOBIN

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The 400kDa hemoglobin from the deep-sea tubeworm, Riftia pachyptila, has the remarkable property of transporting both oxygen and sulfide to the chemoautotrophic bacteria that live in its gut. Our crystal structure of this molecule (Flores et al., 2005, Proc. Natl. Acad. Sci. 102, 2713-2718) revealed both a novel assembly of subunits and unexpected bound zinc ions. We have carried out biochemical experiments that suggest, contrary to the prevailing dogma, that these zinc ions are directly involved in binding sulfide. In order to test this hypothesis, and the alternative one suggesting binding at cysteine residues, we have grown crystals of this molecule in the presence of sulfide under anaerobic conditions. Synchrotron diffraction data collection is required to obtain sufficient resolution from these crystals to permit localizing bound sulfide.