The discovery of chlorophyll f-containing photosystems, with their long-wavelength photochemistry, represented a distinct, low-energy paradigm for oxygenic photosynthesis. Structural studies on chloro...

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

Metal-dependent formate dehydrogenases (FDHs) catalyze, under mild conditions, the reversible reduction of CO2 to formate, a versatile C1 feedstock that can contribute to a carbon-neutral economy. Metal-dependent FDHs are the most widespread selenoproteins found in bacteria, and around 44% of them include selenocysteine (Sec) as a ligand to the Mo/W active site. In the sulfate-reducer Nitratidesulfovibrio vulgaris Hildenborough, the main FDH responsible for CO2 reduction is the W/Sec-dependent FdhAB, which is among the most active CO2 reductases reported so far. In contrast to most metal-dependent FDHs, this enzyme is relatively O2-tolerant and can be purified aerobically. In this work, we evaluated the role of Sec in the catalytic and stability properties of the W/Sec-FdhAB. For that, a Sec-to-Cys variant (U192C) was created, its catalytic and spectroscopic properties were characterized, and its crystal structure was determined. Sec substitution by Cys strongly affects activity, decreases the KM for formate, and increases susceptibility to O2. While Sec-to-Cys replacement induces only weak changes of the WV EPR signals, using 77Se-labeled enzyme, we could show that Sec undoubtedly coordinates the W metal in the WV redox state. The crystal structure of U192C confirmed previous findings on the redox switch mechanism of activation and protection of FdhAB, while revealing a putative catalytic intermediate of FdhAB with Arg441 orienting a CO2 substrate analog (probably SO2) in the active site. Overall, the results indicate that Sec plays a critical role in the high activity displayed by W/Sec-FdhAB, and that it may also be involved in or modulate the proton transfer to and from the active site.

The 2.8-Å resolution structure is presented for a chimeric construct of an emerging tick-borne flavivirus, Powassan virus.

Two distantly related methanogens shift the methanogenic pathway under nickel limitation, suggesting that methanogens adapt to changing bioavailability of nickel by rerouting electron flow between two...

Nature Catalysis - Clustering for methane

Two ferredoxins, FdC and FdN, are collectively essential for the process of nitrogen fixation by the iron nitrogenase in R. capsulatus. We explore the biophysical factors, through spectroscopic and s....