AUTHOR=Löffler Maria , Wallerang Kai B. , Venceslau Sofia S. , Pereira Inês A. C. , Dahl Christiane 

TITLE=The Iron-Sulfur Flavoprotein DsrL as NAD(P)H:Acceptor Oxidoreductase in Oxidative and Reductive Dissimilatory Sulfur Metabolism

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.578209

DOI=10.3389/fmicb.2020.578209

ISSN=1664-302X

ABSTRACT=<p>DsrAB-type dissimilatory sulfite reductase is a key enzyme of microbial sulfur-dependent energy metabolism. Sulfur oxidizers also contain DsrL, which is essential for sulfur oxidation in <italic>Allochromatium vinosum</italic>. This NAD(P)H oxidoreductase acts as physiological partner of oxidative-type rDsrAB. Recent analyses uncovered that DsrL is not confined to sulfur oxidizers but also occurs in (probable) sulfate/sulfur-reducing bacteria. Here, phylogenetic analysis revealed a separation into two major branches, DsrL-1, with two subgroups, and DsrL-2. When present in organisms with reductive-type DsrAB, DsrL is of type 2. In the majority of cases oxidative-type rDsrAB occurs with DsrL-1 but combination with DsrL-2-type enzymes is also observed. Three model DsrL proteins, DsrL-1A and DsrL-1B from the sulfur oxidizers <italic>A. vinosum</italic> and <italic>Chlorobaculum tepidum</italic>, respectively, as well as DsrL-2 from thiosulfate- and sulfur-reducing <italic>Desulfurella amilsii</italic> were kinetically characterized. <italic>Da</italic>DsrL-2 is active with NADP(H) but not with NAD(H) which we relate to a conserved YRR-motif in the substrate-binding domains of all DsrL-2 enzymes. In contrast, <italic>Av</italic>DsrL-1A has a strong preference for NAD(H) and the <italic>Ct</italic>DsrL-1B enzyme is completely inactive with NADP(H). Thus, NAD<sup>+</sup> as well as NADP<sup>+</sup> are suitable <italic>in vivo</italic> electron acceptors for rDsrABL-1-catalyzed sulfur oxidation, while NADPH is required as electron donor for sulfite reduction. This observation can be related to the lower redox potential of the NADPH/NADP<sup>+</sup> than the NADH/NAD<sup>+</sup> couple under physiological conditions. Organisms with a <italic>rdsrAB</italic> and <italic>dsrL-1</italic> gene combination can be confidently identified as sulfur oxidizers while predictions for organisms with other combinations require much more caution and additional information sources.</p>