Recombinant human PCSK9 (Human proprotein convertase subtilisin/kexin 9) encompassing amino acids 31-692, which comprise the protodomain, the catalytic, and the C-terminal domains. The construct contains a C-terminal His-tag (6xHis) followed by an Avi-tag™. The protein contains the potent gain of function D374Y mutation. The protein was affinity purified.