Abstract
We have identified and characterized a novel proline- and arginine-rich protein component of lipoproteins, present in up to five sialylated isoforms, in rabbit blood plasma. The pI of the desialylated protein is 5.7. Based upon its N-terminal sequence, a complete cDNA sequence of 555 nucleotides was cloned from rabbit liver. The synthesized protein is predicted to contain 124 amino acids, including a typical signal peptide of 27 residues. The mature protein of 97 amino acids, designated apolipoprotein C-IV, is associated with the lipoproteins of blood plasma, primarily very low density and high density lipoproteins. It contains two potential amphipathic helices characteristic of plasma apolipoproteins and forms discoidal micelles with phosphatidylcholine. Northern analysis shows a single 0.6-kilobase apolipoprotein C-IV mRNA, detected only in the liver, and Southern analysis suggests a single copy gene. Sialylated apolipoprotein C-IV is secreted from transfected mammalian cells. Nucleotide sequence comparisons demonstrate a strong homology to portions of the upstream regions of the mouse and human apolipoprotein C2 genes, within each of which a distinct gene has recently been identified. The nucleotide sequences and the predicted amino acid sequences, as well as corresponding cDNA sequences in the rat and monkey, indicate that the apolipoprotein C4 gene has been highly conserved during mammalian evolution.
Highlights
Trations and, presumably, surface areas of the lipoprotein particles [3]
Those of low molecular mass are generally called “C” apoproteins, of which three are well recognized [2]. These apoproteins are found in triglyceriderich lipoproteins (chylomicrons and very low density lipoproteins (VLDL)1) and high density lipoproteins (HDL), among which they readily transfer according to the relative concen
Isolation and Characterization of ApoC-IV—ApoC-IV was found during a systematic analysis of small molecular weight apoproteins (C apoproteins) of very low density lipoproteins (VLDL) from rabbit blood plasma
Summary
Trations and, presumably, surface areas of the lipoprotein particles [3]. ApoC-I and apoC-II lack carbohydrate, whereas apoC-III has an O-linked carbohydrate moiety containing up to three sialic acid residues [2]. Lipoproteins in blood plasma of mammals contain a variety of protein components, most of which are water-soluble proteins, encoded by a gene family characterized by repeating sequences of amphipathic helices containing 11 or 22 amino acids [1]. Those of low molecular mass (approximately 6 –12 kDa) are generally called “C” apoproteins, of which three are well recognized [2]. The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) U39356
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