Biosynthesis of human preapolipoprotein A-IV.
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Gordon JI, Bisgaier CL, Sims HF, Sachdev OP, Glickman RM, Strauss AW
Biosynthesis of human preapolipoprotein A-IV.
J Biol Chem. 1984 Jan 10;259(1):468-74.
- PubMed ID
- 6706947 [ View in PubMed]
- Abstract
The primary translation product of human intestinal apolipoprotein A-IV mRNA was purified from ascites and wheat germ cell-free systems. Comparison of its NH2-terminal sequence with mature, chylomicron-associated apo-A-IV revealed that apo-A-IV was initially synthesized with a 20-amino acid long NH2-terminal extension: Met-X-Leu-X-Ala-Val-Val-Leu-X-Leu-Ala-Leu-Val-Ala-Val-Ala-Leu-X-X-Ala. Co-translational cleavage of the cell-free product as well as Edman degradation of the stable intracellular form of the protein recovered from Hep G2 cells indicated that this entire 20-amino acid sequence behaved as a signal peptide. There is at least 55% sequence homology between the rat and human apo-A-IV signal peptides and 33% homology between the human A-I and A-IV presegments. Agarose gel chromatography of Hep G2 culture media indicated that neither apo-A-IV nor -A-I is associated with particles that have physical properties resembling any of the plasma lipoprotein density classes. Incubation of plasma with Hep G2 media resulted in transfer of A-I but not A-IV to lipoproteins. Since the NH2 termini of co-translationally cleaved and chylomicron-associated apo-A-IV are identical, it is apparent that 1) this polypeptide does not undergo NH2-terminal post-translational proteolysis like proapo-A-II or proapo-A-I, and 2) regulation of A-IV-lipoprotein interaction is not dependent on any NH2-terminal proteolytic processing event.