Preparation of Large-Volume Crystal of Cellulase Under Microgravity to Investigate the Mechanism of Thermal Stabilization

Enzymatic saccharification of cellulose by cellulases is expected to enable energy-efficient production of soluble sugars from biomass, and thus the catalytic mechanisms of cellulases have been intensively studied. We have shown that mutation of non-catalytic cysteine residues of cellobiohydrolase Cel6A from the basidiomycete Phanerochaete chrysosporium improves the thermal stability of the enzyme. To understand why, we considered visualizing the hydrogen bond network within the mutant enzyme by neutron diffraction analysis. In this study, we first examined the optimum concentration ranges of NaCl and polyethylene glycol to produce the required large-volume crystal, and based on the results, we chose nine sets of conditions for crystallization under microgravity at the International Space Station. A large-volume crystal of the mutant enzyme was obtained successfully.