Tubeworms living near hydrothermal vents and cold seeps in the world's oceans must adapt to sulfide levels that would prove lethal to most aquatic life while simultaneously providing hydrogen sulfide molecules to symbiotic bacteria within their bodies. A Penn State research team, in collaboration with researchers at the University of Massachusetts Medical School in Worcester and in the United Kingdom, reports a new mechanism for sulfide binding in the hemoglobins, the same molecules that carry oxygen to the worm's own cells. The research team reports that zinc ions in the hemoglobin bind hydrogen sulfide, the first example of any hemoglobin incorporating a metal specifically for that purpose.
"The worms need to bind free sulfide so that it doesn't react with oxygen, to reduce sulfide exposure in their tissues, and to provide the sulfide to the bacteria that, as far as we know, provide all of the worm's nutritional needs," says Charles Fisher, professor of biology at Penn State, whose research team includes Penn State graduate assistant Jason Flores, the lead author of the research paper, and William Royer, professor of biochemistry and molecular pharmacology at the University of Massachusetts. "Our discovery, which results from a very multi-disciplinary approach, replaces the current paradigm for the evolution of worm hemoglobin by demonstrating that hydrogen-sulfide molecules are bound by a metal ion rather than by an arrangement of amino acids."