Crystallization and cross-linking of HheG variant M45F-D114C was performed as described before for variant D114C in 200 µL scale. In a vial, 100 µL of a 24 mg mL -1 protein solution were mixed with 100 µL crystallization buffer (10 mM HEPES, pH 7.0, 8% (w/v) PEG4000) and incubated for 24 h at 8 °C. The resulting crystals were collected by centrifugation for 3 min at 400 g and cross-linked for 24 h at 8 °C with 2 mM bis-maleimidoethane (ThermoFisher Scientific) dissvoled in crystallization buffer containing 10% (v/v) dimethylsulfoxide. After cross-linking, CLECs were collected by centrifugation, washed with 200 µL 50 mM Tris•SO4, pH 7.0, and centrifuged again. Obtained CLECs were resuspended in 50 mM Tris•SO4 buffer, pH 7.0 to a concentration of 2 mg mL -1 . Microscopic analysis of the CLECs was performed using microscope SMZ-171-TLED (Moticeurope, Barcelona, Spain).