Expression and purification of soluble human cystatin C in Escherichia coli with maltose-binding protein as a soluble partner

• Expressing recombinant CYSC is difficult in E. coli because of resulting low yield and insufficient purity and insolubility.
• We found that MBP was best at enhancing the soluble expression of CYSC in E. coli.
• We purified the de-tagged CYSC with immobilized metal affinity chromatography and cation-affinity purification.
• The de-tagged CYSC could react specifically with CYSC polyclonal antibody and displayed full biological activity.
• We provide a method to produce large amounts of soluble recombinant human CYSC in E. coli.

Human cystatin C (CYSC) is a 13-kDa endogenous cysteine proteinase inhibitor and was investigated as a replacement for creatinine as a marker of renal function. However, expressing recombinant CYSC is difficult in Escherichia coli because of resulting low yield and insufficient purity and insolubility. Here, we cloned and fused CYSC to the C-terminus of three soluble partners – maltose-binding protein (MBP), glutathione S-transferase (GST) and translation initiation factor 2 domain I (IF2) – to screen for their ability to improve the solubility of recombinant CYSC when expressed in E. coli. MBP was best at enhancing the soluble expression of CYSC, with soluble fractions accounting for 92.8 ± 3.11% of all proteins. For scaled production, we purified the de-tagged CYSC by using a 3C protease-cleaved MBP-T3-CYSC fused protein with immobilized metal affinity chromatography and cation-affinity purification. The molecular weights of the de-tagged CYSC and human natural CYSC were similar, and the former could react specifically with CYSC polyclonal antibody. Moreover, the de-tagged CYSC displayed full biological activity against papain and cathepsin B, which was very similar to that of the human natural CYSC protein standard. We provide a method to produce large amounts of soluble recombinant human CYSC in E. coli.