PPIase independent chaperone-like function of recombinant human Cyclophilin A during arginine kinase refolding

► The inactive four variants can suppress aggregation and improve the activation yield during AK refolding. ► The more efficiency of Q63A in chaperoning AK folding may associate with its more solvent-exposed global structures. ► Surface hydrophobicity and hydrophobic active pocket of rhCyPA are two key factors for chaperoning AK folding. ► Another protein is shown to be chaperoned by CyPA, which is essential to understand the general roles of CyPA in the cell. Whether Cyclophilin A (CyPA) functions as a foldase or a chaperone when assisting protein folding has long been argued. In this study, we engineered four variants of recombinant human Cyclophilin A (rhCyPA), all of which were inactive to tetrapeptide substrate Suc-AAPF-pNA. However, these variants were able to suppress aggregation during arginine kinase (AK) refolding as efficient as wild-type rhCyPA, especially, variant Q63A had even more efficiency to suppress aggregation and improve reactivation yields of AK. These results indicate that rhCyPA have peptidyl–prolyl cis–trans isomerase (PPIase) independent chaperone-like activity during AK folding. In addition, results suggest that surface hydrophobicity of rhCyPA can suppress AK aggregation and binding to rhCyPA hydrophobic active pocket is a prerequisite for chaperoning AK folding.