Biology subjects

Schmidt, F. V.

Publications and source records attributed to Schmidt, F. V..

3 recordsLinked to original sources

bioRxiv2024

Methylthio-alkane reductases use nitrogenase metalloclusters for carbon-sulfur bond cleavage

Methylthio-alkane reductases convert methylated sulfur compounds to methanethiol and small hydrocarbons, a process with important environmental and biotechnological implications. These enzymes are classified as nitrogenase-like enzymes, despite lacking the ability to convert dinitrogen to ammonia, raising fundamental questions about the factors controlling their activity and specificity. Here, we present the first molecular structure of the methylthio-alkane reductase, which reveals large metalloclusters, including the P-cluster and the [Fe8S9C]-cluster, previously only found in nitrogenases. Our findings suggest that distinct metallocluster coordination, surroundings, and substrate channels, determine the activity of these related metalloenzymes. This study provides new insights into nitrogen fixation, sulfur-compound reduction, and hydrocarbon production. We also shed light on the evolutionary history of P-cluster and [Fe8S9C]-cluster-containing reductases emerging prior to nitrogenases.

biochemistry↗

bioRxiv2023

CO2 Reduction by the Iron Nitrogenase Competes with N2 Fixation Under Physiological Conditions

Nitrogenases are the only known enzymes that reduce molecular nitrogen (N2) to ammonia. Recent findings have demonstrated that nitrogenases also reduce the greenhouse gas carbon dioxide (CO2), suggesting CO2 to be a competitor of N2. Intriguingly, nitrogenase isoforms (i.e., molybdenum (Mo), vanadium and iron (Fe) nitrogenase) differ significantly in their ability to reduce CO2, but the mechanisms underlying these differences remain elusive. Here, we study the competing reduction of CO2 and N2 by the two nitrogenases of Rhodobacter capsulatus, the Mo and Fe nitrogenase. Analyzing their full CO2 reduction product spectrum in vitro, we find the Fe nitrogenase almost three-fold more efficient in CO2 reduction than the Mo isoform. Furthermore, the in vitro competition experiments reveal the Fe nitrogenase to be profoundly less selective for the reduction of N2 than the Mo nitrogenase. We observe the same effects in vivo, where adding CO2 drastically increases the doubling times of diazotrophically grown R. capsulatus strains that rely on the Fe nitrogenase. The Fe nitrogenase-dependent R. capsulatus strains reduce CO2 to methane under physiological conditions, highlighting the potential of the Fe nitrogenase for the biotechnological conversion of CO2 into value-added compounds. Furthermore, both products are secreted into the surrounding, potentially influencing the composition of microbial communities in Mo-deficient environments.

biochemistry↗

bioRxiv2023

Structural Insights into the Iron Nitrogenase Complex

Nitrogenases are best known for catalysing the reduction of dinitrogen to ammonia at a complex metallic cofactor. Recently, nitrogenases were shown to reduce carbon dioxide (CO2) and carbon monoxide to hydrocarbons, offering a pathway to recycle carbon waste into hydrocarbon products. Among the nitrogenase family the iron nitrogenase is the isozyme with the highest wildtype activity for the reduction of CO2, but the molecular architecture facilitating these activities remained unknown. Here, we report a 2.35-[A] cryogenic electron microscopy structure of the Fe nitrogenase complex from Rhodobacter capsulatus, revealing an [Fe8S9C-(R)-homocitrate]-cluster in the active site. The enzyme complex suggests that the AnfG-subunit is involved in cluster stabilisation, substrate channelling and confers specificity between nitrogenase reductase and catalytic components. Moreover, the structure highlights a different interface between the two catalytic halves of the iron and the molybdenum nitrogenase, potentially influencing the intra-subunit communication and thus the nitrogenase mechanism.

biochemistry↗