Identification and Structure Determination of a Bacterial Hydrosulfide Ion Channel

Though it is believed to have been critical to the origin of life on Earth, hydrogen sulfide (H2S) still plays a prominent role in physiology and cellular signaling. Its undissociated form, hydrosulfide ion (HS-), is a major metabolite in bacterial anaerobic fermentation. While toxicity due to HS- and H2S, has been extensively characterized, the molecular mechanism for HS- transport across the cell membrane is unknown. Through a combination of genetic, biochemical and functional approaches, we have identified a hydrosulfide ion channel (HSC) in the pathogen Clostridium difficile. The HS- channel is a member of the formate-nitrite-transport (FNT) family, and ∼50 HSC genes form a third subfamily besides those for formate and for nitrite. In addition to HS- ions, HSC is also permeable to formate and nitrite. Crystallographic studies revealed an HSC structure that is similar to that of the formate channel FocA [1], with an aquaporin fold that is arranged into a pentamer. Structural and biochemical characterization showed that the ion-selectivity filter is located in the center of the protomer.Reference:1. Waight AB, Love J, Wang DN: Structure and mechanism of a pentameric formate channel. Nat Struct Mol Biol 2010, 17:31-37.