Expression and purification of recombinant human apolipoprotein A-II in Pichia pastoris

Apolipoprotein A-II (ApoA-II) is the second most abundant protein constituent of high-density lipoprotein (HDL). The physiologic role of ApoA-II is poorly defined. ApoA-II may inhibit lecithin:cholesterol acyltransferase and cholesteryl-ester-transfer protein activities, but may increase the hepatic lipase activity. ApoA-II may also inhibit the hepatic cholesteryl uptake from HDL probably through the scavenger receptor class B type I depending pathway. Interpretation of data from transgenic and knockout mice of genes involved in lipoprotein metabolism has been often complicated as clinical implications because of species difference. So it is important to obtain human ApoA-II for further studies about its functions. In our studies, Pichia pastoris expression system was first used to express a high-level secreted recombinant human ApoA-II (rhApoA-II). We have cloned the cDNA encoding human ApoA-II and achieved its high-level secreting expression with a yield of 65 mg/L of yeast culture and the purification process was effective and easy to handle. The purified rhApoA-II can be used to further study its biological activities.