Hydrogen bioelectrogeneration with pH-resilient and oxygen-tolerant cobalt apoenzyme-saccharide

Abstract

Hydrogenases are enzymes that catalyze the reversible conversion of protons to hydrogen gas, using earth-abundant metals such as nickel and/or iron. This characteristic makes them promising for sustainable energy applications, particularly in clean hydrogen production. However, their widespread use faces challenges, including a limited pH range and susceptibility to oxygen. In response to these issues, SacCoMyo is introduced as an artificial enzyme. SacCoMyo is designed by replacing the native metal in the myoglobin (Myo) scaffold with a hydroxocobalamin (Co) porphyrin core and complemented by a protective heteropolysaccharide-linked (Sac) shell. This engineered protein proves to be resilient, maintaining robust functionality even in acidic environments and preventing denaturation in a pH 1 electrolyte. The cobalt porphyrin core of SacCoMyo reduces the activation overpotential for hydrogen generation. A high turnover frequency of about 2400 H₂ s⁻¹ is demonstrated in the presence of molecular oxygen, showcasing its potential in biohydrogen production and its ability to overcome the limitations associated with natural hydrogenases.