Sulfurtransferases as essential players during dissimilatory sulfur oxidation

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Persulfide groups are chemically versatile and participate in a wide array of biochemical pathways. Whilst it is well documented that persulfurated proteins supply a number of important and elaborate biosynthetic pathways with sulfane sulfur, this project aims at exploring the exact contribution of sulfurtransferase-catalyzed reactions to oxidative sulfur metabolism. We already collected basic information on the extensive sulfur-trafficking system occurring in the cytoplasm of sulfur oxidizing bacteria pursuing the Dsr (dissimilatory sulfite reductase) pathway of sulfur oxidation. In addition, we gathered biochemical and bioinformatic evidence pointing at the so-called heterodisulfide-reductase (Hdr) -like system as a wide-spread alternative sulfite-generating system in sulfur-oxidizing prokaryotes. Sulfur-trafficking was established to also be of pivotal importance in organisms pursuing this pathway and thus emerges as a central and common element during dissimilatory sulfur oxidation. The present project will address two major questions: (1.) What is the exact series of events during protein-bound sulfur oxidation via the Dsr pathway? (2.) Does the Hdr-like system indeed work a sulfite-generating system and how exactly are sulfur transfer reactions involved? To solve these questions, biochemical characterization of proteins (reconstitution of enzyme systems in vitro, identification of substrates and products), protein interaction studies, and gene expression profiling will be combined with gene inactivation and complementation studies (growth experiments with wild type, defined mutant and complemented mutants strains) as well as with molecular genetic techniques. The genetically accessible purple sulfur bacterium Allochromatium vinosum will serve as the model organism for the studies on sulfur transfer reactions and oxidation of protein-bound sulfur via the Dsr system, while Thioalkalivibrio and Thiorhdospira species as well as the genetically accessible Alphaproteobacterium Hyphomicrobium denitrificans will be used for elucidating sulfur transfer reactions and oxidation of protein-bound sulfur associated with the Hdr-like system. Ultimately, our results are expected to completely unravel the networks of sulfur transfer reactions occurring in sulfur oxidizing prokaryotes, to add new reactions and proteins to persulfide group biochemistry and to clarify a new pathway of sulfur oxidation.