[SCAN] Two is company, three is a crowd: a tale on thiosulfate dehydrogenases

SCAN

Title: Two is company, three is a crowd: a tale on thiosulfate dehydrogenases

Speaker: José Brito, ITQB NOVA

Affiliation: Margarida Archer Lab

Abstract:

Thiosulfate is an important intermediate in the biogeochemical sulfur cycle. It is formed by oxidation of sulfide in soils and sediments and is also the product of sulfide detoxification in the animal gut.

Thiosulfate dehydrogenases (TsdAs) catalyze the reversible formation of a sulfur-sulfur bond between the sulfane atoms of two thiosulfate molecules, yielding tetrathionate and releasing two electrons. TsdA homologues are wide-spread among bacteria, agreeing with reports of tetrathionate formation not only by specialized sulfur oxidizers but also by many
chemoorganoheterotrophic bacteria. In the purple sulfur bacterium Allochromatium vinosum, thiosulfate is oxidized by two different pathways: TsdA catalyzes the one-step oxidation to tetrathionate, and the Sox system in conjunction with the Dsr system oxidizes thiosulfate completely to sulfate.
Although the oxidative condensation of two thiosulfate anions to tetrathionate constitutes a well documented and significant part of the natural sulfur cycle, little is known about the enzymes catalyzing this reaction. To fill this gap, the gene coding for the thiosulfate
dehydrogenase enzyme from Allochromatium vinosum was recombinantly expressed in Escherichia coli and its product purified, kinetic and spectroscopically characterized.

Morevoer, we have determined its crystallographic structure in several redox states. More recently, we have also determined the crystal structure of the enzymes TsdA from Campylobacter jejuni and Marichromatium purpuratum.
In this talk, we will provide an overview of the work done and the results obtained so far which led us to propose a new reaction mechanism for these enzymes.