title: Synthesis, transport, and processing of apolipoproteins of high density lipoproteins.
abstract: Cell biology methods have greatly influenced the elucidation of the biosynthetic pathways of apolipoproteins. In vitro and tissue culture systems allow the study, to a large extent, of the process of synthesis, intracellular processing, secretion, and extracellular processing of the major high density lipoprotein apoproteins apoA-I and A-II and also of a minor component, apoA-IV. Whereas the latter apoprotein is equipped only with a signal sequence, the primary translation products of apoA-I and apoA-II carry N-terminal extensions of preprosequence of 24 amino acids for apoA-I and 23 amino acid residues for apoA-II. The pro-form of apoA-I characterized by a hexapeptide extension is completely stable intracellularly and is secreted as such. The pro-form is further processed by a serum protease specific for an unusual -Gln-Gln-Asp-Glu-sequence site. Pro-apoA-II, a pentapeptide sequence, is partially processed intracellularly to its mature form and secreted together with the residual pro-form. The cleavage site of pro-apoA-II is characterized by two basic amino acid residues Arg-Arg, present also in other known pro-proteins. The biological function of the N-terminal pro-sequences and details of their final processing by the serum protease(s) have yet to be established.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001053:Apolipoproteins / Q000378:metabolism*; D001054:Apolipoproteins A / Q000378:metabolism; D001693:Biological Transport, Active; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
chemical_list: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001053:Apolipoproteins; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; D012333:RNA, Messenger