Intermediates in the Sox sulfur oxidation pathway are bound to a sulfane conjugate of the carrier protein SoxYZ

Abstract

The Sox pathway found in many sulfur bacteria oxidizes thiosulfate to sulfate. Pathway intermediates are covalently bound to a cysteine residue in the carrier protein SoxYZ. We have used biochemical complementation by SoxYZ-conjugates to probe the identity of the intermediates in the Sox pathway. We find that unconjugated SoxYZ and SoxYZ-S-sulfonate are unlikely to be intermediates during normal turnover in disagreement with current models. By contrast, conjugates with multiple sulfane atoms are readily metabolised by the Sox pathway. The most parsimonious interpretation of these data is that the true carrier species in the Sox pathway is a SoxYZ-S-sulfane adduct.

Comparison of sulfide‐oxidizing Sulfurimonas strains reveals a new mode of thiosulfate formation in subsurface environments

“…The SOX enzyme complex in Paracoccus pantotrophus , a model alphaproteobacterial sulfur oxidizer, requires four enzymes for full in vitro activity. These are the c‐type cytochromes SoxAX, the sulfur compound binding module SoxYZ, the sulfate thiol esterase SoxB and a sulfur dehydrogenase Sox(CD) 2 (Friedrich et al ., ; Rother et al ., ; Grabarczyk and Berks, ). During the oxidation cycle, the sulfur intermediates are covalently linked to a cysteine residue in the SoxY subunit facilitated by SoxAX.…”

“…During the oxidation cycle, the sulfur intermediates are covalently linked to a cysteine residue in the SoxY subunit facilitated by SoxAX. Depending on the oxidation state of the terminal cysteine‐bound sulfur atom SoxB will hydrolytically release sulfate either with or without Sox(CD) 2 performing an initial oxidation of the cysteine persulfide to a sulfonate (Friedrich et al ., ; Grabarczyk and Berks, ). Therefore, in green and purple sulfur bacteria that carry only the soxXYZAB genes, the absence of Sox(CD) 2 leads to S 0 accumulation during thiosulfate oxidation (Hensen et al ., ; Frigaard and Dahl, ).…”

Transcriptomic and proteomic insight into the mechanism of cyclooctasulfur‐ versus thiosulfate‐oxidation by the chemolithoautotroph Sulfurimonas denitrificans

“…Based on our observations on the differential abundance of the SOX proteins during growth on thiosulfate versus S 8 and previous results (Friedrich et al ., , ; Sauvé et al ., ; Grabarczyk and Berks, ), we propose a sulfur oxidation model for the oxidation of S 8 by S. denitrificans that does not involve the SoxABXY 1 Z 1 protein complex (Fig. ).…”

“…Future experiments need to be carried out to differentiate between these options. Thiosulfate oxidation by S. denitrificans proceeds mainly as proposed in the current sulfur oxidation model (Friedrich et al, , 2005Grabarczyk and Berks, 2017). First, thiosulfate is activated via SoxXA and bound to a cysteine residue of SoxY in the SoxYZ 1 complex, followed by the hydrolysis of the outer sulfonate group of the bound thiosulfate by SoxB .…”

“…In the currently accepted model of the SOX multienzyme system, SoxYZ is the sulfur carrier and binds various reduced sulfur compounds covalently to a cysteine residue on SoxY, which is coordinated by SoxAX (Quentmeier and Friedrich, ; Dahl and Prange, ; Grabarczyk and Berks, ). SoxB then hydrolyzes sulfate (SO 4 2− ) to generate a cysteine‐persulfide left on SoxY.…”