SDS–PAGE monitoring of the overexpression and purification of SeMet XC6012. Lane 1, protein molecular-weight markers (kDa); lane 2, whole cell lysate before IPTG induction; lane 3, whole cell lysate after IPTG induction; lane 4, supernatant of His6-tagged XC6012; lane 5, purified XC6012 after TEV cleavage.