International Journal of Molecular Sciences Review Heterologous Hydrogenase Overproduction Systems for Biotechnology—An Overview Qin Fan 1 , Peter Neubauer 1 , Oliver Lenz 2 and Matthias Gimpel 1,* 1 Institute of Biotechnology, Technical University of Berlin, Ackerstraße 76, 13355 Berlin, Germany;
[email protected] (Q.F.);
[email protected] (P.N.) 2 Department of Chemistry, Technical University of Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany;
[email protected] * Correspondence:
[email protected] Received: 14 July 2020; Accepted: 14 August 2020; Published: 16 August 2020 Abstract: Hydrogenases are complex metalloenzymes, showing tremendous potential as H2-converting redox catalysts for application in light-driven H2 production, enzymatic fuel cells and H2-driven cofactor regeneration. They catalyze the reversible oxidation of hydrogen into protons and electrons. The apo-enzymes are not active unless they are modified by a complicated post-translational maturation process that is responsible for the assembly and incorporation of the complex metal center. The catalytic center is usually easily inactivated by oxidation, and the separation and purification of the active protein is challenging. The understanding of the catalytic mechanisms progresses slowly, since the purification of the enzymes from their native hosts is often difficult, and in some case impossible. Over the past decades, only a limited number of studies report the homologous or heterologous production of high yields of hydrogenase. In this review, we emphasize recent discoveries that have greatly improved our understanding of microbial hydrogenases. We compare various heterologous hydrogenase production systems as well as in vitro hydrogenase maturation systems and discuss their perspectives for enhanced biohydrogen production.