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. Additionally, activities of hydrogenases isolated from either recombinant organisms or in vivo/in vitro maturation approaches were systematically compared, and future perspectives for this research area are discussed.
Highlights
The world’s still increasing hunger for energy and the resulting excessive use of fossil fuels is a major reason for environmental pollution and global warming
Over the past few years, enormous progress has been made in our understanding of hydrogenase structure, function and their applications in biohydrogen production in vivo or in vitro mediated by recombinantly produced enzymes
Work on [NiFe]-hydrogenases in particular has shown that many microbes have developed a natural solution to confer these enzymes’ O2 tolerance and catalytic bias
Summary
The world’s still increasing hunger for energy and the resulting excessive use of fossil fuels is a major reason for environmental pollution and global warming. Protein purified from anaerobically grown cells showed a 1.8-fold higher specific hydrogenase activity when compared to native SH isolated from the native host R. eutropha [130,143] This platform based on synthetic biology provides a novel direction to produce recombinant [NiFe]-hydrogenases and facilitate directed evolution approaches to optimize the enzymes and their reaction conditions. The studies described above advanced our understanding of how these accessory proteins work together in active site assembly This innovative in vitro maturation system for [NiFe]-hydrogenases provides an appealing strategy to engineer hydrogenases with desired properties, e.g., improved O2 tolerance or incorporation of alternative catalytic metal ion centers, which, in turn, offers the possibility for creating new enzymatic reactions. The complex process of post-translational maturation of [NiFe]hydrogenases requires further exploration
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