One isoform for one task? The second hydrogenase of Chlamydomonas reinhardtii prefers hydrogen uptake

Abstract Gaining knowledge about the algal hydrogen metabolism is prerequisite for the biotechnological exploitation of photosynthetic H2 production. Model organism Chlamydomonas reinhardtii encodes two [FeFe]-hydrogenases, which are individually capable of catalysing the reversible reduction of protons to molecular hydrogen. While physiological results indicated that HYDA1, connected to the photosynthetic electron transfer pathway via plant-type ferredoxin PETF, is accountable for a major part of algal H2 evolution, the role of HYDA2 in the algal metabolism is not understood yet. Herein, a comprehensive screening of enzymatic attributes was conducted, revealing that the two enzymes differ in their affinity to oxidised PETF. Notably, utilising protein film voltammetry, a higher catalytic preference of HYDA2 to consume H2 was observed. Site directed exchange mutagenesis revealed the contribution of a hydroxyl group in place of threonine 226, present in HYDA1, but not in HYDA2, potentially influencing the electronic properties of the active site, thereby fine-tuning catalytic function.