Engineering and refolding of a novel trimeric fusion protein TRAIL-collagen XVIII NC1

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is considered to be a promising anticancer agent because its active form TRAIL trimer is able to induce apoptosis in different tumor cell lines while sparing normal cells. However, TRAIL trimer possesses a short half-life and low stability, which turns out to be a major obstacle for the development of clinical trials. In our present study, we constructed a recombined TRAIL trimer by genetic fusion of non-collagenous domain (NC1) of human collagen XVIII or its trimerization domain (TD) to C-terminus of TRAIL via a flexible linker, and then refolded the fusion proteins using a two-step refolding approach, namely a combination of dilution and gel filtration chromatography. As a result, both recombinant proteins, TRAIL-NC1 and TRAIL-TD, were expressed in Escherichia coli as inclusion bodies, and they exhibited difficultly to refold efficiently by conventional methods. Thereby, we applied a modified two-step refolding approach to refold fusion proteins. More than 55 % of TRAIL-NC1 and 90 % of TRAIL-TD protein activity was recovered during the two-step refolding approach, and their stability was also increased significantly. Also, size exclusion chromatography showed refolded TRAIL-NC1 was a trimer while TRAIL-TD, hexamer. However, both of them exerted good apoptosis activity on NCI-H460 cells.