Homologous and heterologous overexpression in Clostridium acetobutylicum and characterization of purified clostridial and algal Fe-only hydrogenases with high specific activities

Clostridium acetobutylicum ATCC 824 was selected for the homologous overexpression of its Fe-only hydrogenase and for the heterologous expressions of the Chlamydomonas reinhardtii and Scenedesmus obliquus HydA1 Fe-only hydrogenases. The three Strep tag H-tagged Fe-only hydrogenases were isolated with high specific activities by two-step column chromatography. The purified algal hydrogenases evolve hydrogen with rates of around 700 mu mol H-2 min(-1) mg(-1), while HydA from C. acetobutylicum (HydA(Ca)) shows the highest activity (5,522 mu mol H-2 min(-1) mg(-1)) in the direction of hydrogen uptake. Further, kinetic parameters and substrate specificity were reported. An electron paramagnetic resonance (EPR) analysis of the thionin-oxidized HydA(Ca) protein indicates a characteristic rhombic EPR signal that is typical for the oxidized H cluster of Fe-only hydrogenases.