[NiFe]-Hydrogenases of <i>Ralstonia eutropha</i> H16: Modular Enzymes for Oxygen-Tolerant Biological Hydrogen Oxidation

Abstract

Recent research on hydrogenases has been notably motivated by a desire to utilize these remarkable hydrogen oxidation catalysts in biotechnological applications. Progress in the development of such applications is substantially hindered by the oxygen sensitivity of the majority of hydrogenases. This problem tends to inspire the study of organisms such as Ralstonia eutropha H16 that produce oxygen-tolerant [NiFe]-hydrogenases. R. eutropha H16 serves as an excellent model system in that it produces three distinct [NiFe]-hydrogenases that each serve unique physiological roles: a membrane-bound hydrogenase (MBH) coupled to the respiratory chain, a cytoplasmic, soluble hydrogenase (SH) able to generate reducing equivalents by reducing NAD⁺ at the expense of hydrogen, and a regulatory hydrogenase (RH) which acts in a signal transduction cascade to control hydrogenase gene transcription. This review will present recent results regarding the biosynthesis, regulation, structure, activity, and spectroscopy of these enzymes. This information will be discussed in light of the question how do organisms adapt the prototypical [NiFe]-hydrogenase system to function in the presence of oxygen.

Probing the Origin of the Metabolic Precursor of the CO Ligand in the Catalytic Center of [NiFe] Hydrogenase

“…R. eutropha harbors at least three well characterized [NiFe] hydrogenases that sustain growth on H 2 as the energy source and O 2 as the terminal electron acceptor. The energy collected from this process can be used for autotrophic CO 2 fixation (25). All three hydrogenases of R. eutropha are catalytically active in the presence of O 2 and, hence, rely on an O 2 -tolerant maturation process (7).…”

“…All three hydrogenases of R. eutropha are catalytically active in the presence of O 2 and, hence, rely on an O 2 -tolerant maturation process (7). The RH of R. eutropha functions as an H 2 sensor and controls H 2 -dependent synthesis of the two energy-converting [NiFe] hydrogenases (25).…”

Discovery of [NiFe] Hydrogenase Genes in Metagenomic DNA: Cloning and Heterologous Expression in Thiocapsa roseopersicina

“…Thus, transfer of O 2 -tolerant [NiFe] hydrogenases into cyanobacteria might be one approach to overcome this O 2 sensitivity issue. A small number of O 2 -tolerant hydrogenases has been identified (9,21,47). However, they tend to favor H 2 uptake over evolution.…”

Third-generation feed stocks for the clean and sustainable biotechnological production of bulk chemicals: synthesis of 2-hydroxyisobutyric acid

“…To confirm the capacity of the chosen system for 2-HIB synthesis, a fructose pre-grown culture was used to inoculate the cultivation apparatus. A gas stream containing 25% to 50% H 2 , 15% to 30% CO 2 , and 10% to 20% O 2 was supplied as a growth substrate, resulting in the induction of the enzymes required for chemo-litho-autotrophic growth, especially hydrogenases [58,59], and for carbon dioxide fixation [60]. Under these conditions, growth proceeded at a rate of about 0.066/h until the nitrogen source was exhausted, attaining a final biomass concentration of approximately 2.0 g/L (Figure 2).…”