A Deletion of Signal Peptide in Recombinant Murine Gamma-herpesvirus 68 M3 Protein Enhances Its Binding Affinity to CCL5 Chemokine and Increases Its Yield from Insect Cells

Objective: The M3 protein encoded by murine gamma-herpesvirus 68 (MHV-68) was the first secreted protein identified in herpesvirus. This protein is unique in its ability to bind a broad-spectrum of chemokines from all four subfamilies, thus it has been proposed to be a potential gene therapy candidate for controlling the overactive inflammatory responses of some human inflammatory diseases. Methods: We prepared MHV-68 M3del protein with a deletion of its signal peptide (M3del) and full-length MHV-68 M3 protein (M3) using a baculovirus-mediated insect cell expression system and confirmed their specificity by Western blot using newly prepared mouse monoclonal anti-M3 antibody 1/27. Binding affinity of both proteins to human CCL5 and CXCL8 chemokine was examined by ELISA. Results: M3del and M3 displayed affinity to both chemokines tested. M3 del concentration sufficient to bind 25% of CCL5 was two times smaller than that of M3 (IC25=3.5 nmol/l vs. 6.1 nmol/l). In contrary, the values of IC25 for CXCL8 for M3del and M3 were comparable (IC25=13.8 nmol/l vs. 13.3 nmol/l. We have found that the absence of signal peptide strongly affects the yield of recombinant M3 protein. The yields of M3del and M3 were in an unbalanced ratio of 67 to 1. Conclusions: The results suggest that the absence of signal peptide in recombinant MHV-68 M3 protein allows increased binding activity of the protein to CCL5 but not to CXCL8, and even a very large increase in its yield from insect cells.