Abstract
Anaerobic ammonium-oxidizing (anammox) bacteria convert nitrite and ammonium via nitric oxide (NO) and hydrazine into dinitrogen gas by using a diverse array of proteins, including numerous c-type cytochromes. Many new catalytic and spectroscopic properties of c-type cytochromes have been unraveled by studies on the biochemical pathways underlying the anammox process. The unique anammox intermediate hydrazine is produced by a multiheme cytochrome c protein, hydrazine synthase, through the comproportionation of ammonium and NO and the input of three electrons. It is unclear how these electrons are delivered to hydrazine synthase. Here, we report the discovery of a functional tetraheme c-type cytochrome from the anammox bacterium Kuenenia stuttgartiensis with a naturally-occurring contracted Cys-Lys-Cys-His (CKCH) heme-binding motif, which is encoded in the hydrazine synthase gene cluster. The purified tetraheme protein (named KsTH) exchanged electrons with hydrazine synthase. Complementary spectroscopic techniques revealed that this protein harbors four low-spin hexa-coordinated hemes with His/Lys (heme 1), His/Cys (heme 2), and two His/His ligations (hemes 3 and 4). A genomic database search revealed that c-type cytochromes with a contracted CXCH heme-binding motif are present throughout the bacterial and archaeal domains in the tree of life, suggesting that this heme recognition site may be employed by many different groups of microorganisms.
Highlights
Anaerobic ammonium-oxidizing bacteria convert nitrite and ammonium via nitric oxide (NO) and hydrazine into dinitrogen gas by using a diverse array of proteins, including numerous c-type cytochromes
We report the discovery of a functional tetraheme c-type cytochrome from the anammox bacterium Kuenenia stuttgartiensis with a naturally-occurring contracted Cys–Lys–Cys–His (CKCH) heme-binding motif, which is encoded in the hydrazine synthase gene cluster
Heme 1 was attached to the protein backbone via a CKCH motif and was the first observed naturally occurring representative of such a contracted hemebinding sequence
Summary
Anaerobic ammonium-oxidizing (anammox) bacteria convert nitrite and ammonium via nitric oxide (NO) and hydrazine into dinitrogen gas by using a diverse array of proteins, including numerous c-type cytochromes. We report the discovery of a functional tetraheme c-type cytochrome from the anammox bacterium Kuenenia stuttgartiensis with a naturally-occurring contracted Cys–Lys–Cys–His (CKCH) heme-binding motif, which is encoded in the hydrazine synthase gene cluster. We demonstrated that this contracted heme-binding motif bound a heme c cofactor; we assessed whether this contracted heme coordination resulted in any distinct properties for the heme, and we probed the interaction between purified KsTH and hydrazine synthase
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have