Primary structure of apolipoprotein A-II from inbred mouse strain BALB/c

The primary structure of apolipoprotein A-II (apoA-II) isolated from the plasma high density lipoprotein (HDL) fraction of the inbred mouse strain BALB/c is described in this work. The complete 78 amino acid protein sequence was determined by proteolytic fragmentation, gas-phase microsequence analysis, and fast atom bombardment (FAB) mass spectrometry. The apolipoprotein has a calculated molecular weight of 8,715 and a net negative charge conveyed by ten acidic and eight basic amino acid residues. There exists a 55% amino acid sequence homology between the BALB/c mouse apoA-II and human apoA-II. Unlike human plasma apoA-II, which exists as a disulfide dimer, BALB/c apoA-II lacks cysteine and is a monomer. BALB/c apoA-II contains one residue each of histidine and arginine, neither of which are found in the human A-II protein. Chou and Fasman analysis of the BALB/c apoA-II primary structure predicts approximately 68% alpha-helical potential compared with a 62% potential for human apoA-II. The alpha-helical domains are structurally amphipathic, generating a polar and an apolar face consistent with the proposed models describing apolipoprotein-phospholipid interaction.