Optimal conditions for expressing a complement component 3b functional fragment (α2-macroglobulin receptor) gene from Epinephelus coioides in Pichia pastoris

The α2-macroglobulin receptor (α2MR) is a major domain of complement component 3b, which may play an important role in regulating the downstream complement system in teleosts. In order to characterize the domain thoroughly larger than currently available quantities are required. Thus, in this study the Epinephelus coioides α2MR (Ec-α2MR) was expressed and secreted by the methylotrophic yeast Pichia pastoris with variations in pH and induction time to identify optimal production conditions. At pH 5.5 with 48 h induction 13 mg of Ec-α2MR (ca. 90% purity) was obtained from 500 ml of culture. The Ec-α2MR protein product was validated by MALDI-TOF MS sequence analysis, and both Western blotting and ELISAs demonstrated that it possessed the expected activity, binding to C3b or C3b homolog antibodies, and thus can be used for future studies of the interactions and functions of complement proteins in teleosts.