Amino Acid Sequence Of Apolipoprotein Research Articles

Apolipoprotein E4 Prevalence in Different Canine Breeds

Three common isoforms of apolipoprotein E (APOE) are found in most populations: E2, E3, and E4, the Ε4 isoform has been proven to be associated with Alzheimer’s disease (AD) and coronary heart disease (CHD). In human, attributable risk due to APOE4 varies by region and by race/ethnicity. To gain a better understanding of APOE genetic polymorphism in canines, we aimed to explore the prevalence of apolipoprotein E isoform distribution in five different pure breeds (Thai Ridgeback, Golden Retriever, Labrador Retriever, Bulldog, Shih Tzu) using APOE gene sequencing analysis. Our results showed a very high homology of apolipoprotein E sequences in the examined canines, including human APOE3 and human APOE4, ranging from 71.76-100 and 78.23-100% identity and similarity, respectively. All investigated canine breeds could be identified as APOE4 carriers due to the presence of arginine at the positions 112 and 158, which correspond to APOE4 of human. This indicates that APOE polymorphism was not present in the genome of all examined canine breeds. It is possible that the finding of canine apolipoprotein E4 may be important in predicting an increased risk of pathophysiological development of neurodegenerative diseases and coronary heart disease. Our reconstructed phylogenetic tree showed two well-defined clusters based on the amino acid sequence of apolipoprotein E, including canine and human group. Further studies should explore if these different clusters are associated with diseases.

Apolipoprotein E isoforms, serum cholesterol, and cancer. 1986.

tumour may have depressed cholesterol levels though in others the relation was found when serum cholesterol had been measured many years before the cancer was diagnosed. The relation is probably not explained by diet, because in the Seven Countries Study cohorts with widely different diets and corresponding differences in mean cholesterol levels experienced similar mean cancer rates. 2,3 On the other hand, within each region cancer incidence was higher in men with a serum cholesterol in the lowest part of the cholesterol distribution for that country. 3 Thus, naturally low cholesterol levels are sometimes associated with increased cancer risk. 1,3 Differences in the aminoacid sequence of apolipoprotein E (apo E) are major determinants of differences in plasma cholesterol levels within a population. Apo E has a key role in the clearance of cholesterol from plasma. 4 The synthesis of apo E is under the control of three independent alleles, located at a single gene locus, coding for the major isoforms E-2, E-3, and E-4 with respective population frequencies of about 8, 77, and 15%. 5 The homozygous E-3/E-3 is the most common phenotype encountered and E-2/E-2 is the least common. From apo E-2 to apo E-3, one cysteine residue is replaced by arginine, and from apo E-3 to apo E-4 another cysteine residue is replaced. As a result the avidity of apo E containing lipoproteins for lipoprotein receptors increases from apo E-2 to apo E-3 to apo E-4. In several populations, 6‐8 including the Finns and the Japanese (Dr G Utermann, personal communication), the gradient in serum cholesterol levels in the population is associated with a gradient in apo E phenotype, E-2 being associated with lower serum low-density lipoprotein and total cholesterol levels than E-3 and E-4. Thus, if a naturally low cholesterol favours tumour growth, then subjects with the E-2/E-2 or E-2/E-3 phenotype should have an increased risk of cancer. Unlike most other indices of lipid metabolism, apolipoprotein aminoacid sequences are not disturbed by disease, and the apo E phenotype found in a patient will have been present since birth. A comparison of apo E phenotypes in cancer patients with those in matched controls might thus shed light on the relation between low cholesterol and cancer. If it is causal then the E-2 allele should be more common among patients and E-3 and E-4 more common among controls. On the other hand, equal distribution of apo E phenotypes among cases and controls would suggest that the association between low cholesterol and cancer is spurious. Measurement of apo E phenotype by isoelectric focusing of plasma is a routine determination in lipid laboratories; epidemiologists interested in cholesterol and cancer should include it in their studies.

Identification of glycoprotein IIb as the lipoprotein(a)-binding protein on platelets. Lipoprotein(a) binding is independent of an arginyl-glycyl-aspartate tripeptide located in apolipoprotein(a).

Lipoprotein(a) [Lp(a)] plays an important role in atherosclerosis. The amino acid sequence of apolipoprotein(a) [apo(a)] reveals an arginyl-glycyl-aspartate (RGD) tripeptide that is the consensus sequence for binding of adhesive plasma proteins of the fibrinolytic system, such as fibrinogen and von Willebrand factor, to the platelet membrane glycoprotein IIb-IIIa (GPIIb-IIIa) complex. Therefore, we undertook the present study to further investigate the role of Lp(a) in hemostasis. Binding of 125I-Lp(a) to a single platelet membrane-associated protein (137 +/- 6 kD) comigrating with platelet GPIIb (140 kD) was found to be specific, saturable, and Ca2+ independent. Binding of 125I-Lp(a) to resting human blood platelets was saturable, insensitive to temperature, and independent of the apo(a) isoform (B, S1 through S3). Scatchard analysis revealed a Kd of 7.2 +/- 1.8 x 10(-9) mol/L, with 729 +/- 313 Lp(a) molecules bound per platelet. Monoclonal anti-GPIIb IgG diminished Lp(a) binding by approximately 80%, monoclonal anti-GPIIb-IIIa IgG by 60%, and anti-GPIIIa IgG by just 15%. 125I-Lp(a) binding was competitively inhibited to the same extent by either unlabeled Lp(a) or fibrinogen. Low- and high-density lipoproteins were much weaker competitors. A polyclonal antibody raised against the RGDGQSYRGT sequence of apo(a) was used to verify the presence of an RGD sequence in the different Lp(a) preparations investigated. However, two lines of evidence indicated that the RGD sequence is not the binding domain mediating Lp(a) binding to platelets. First, incubation of platelets with isolated RGD tripeptide did not influence Lp(a) binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of synthetic peptides of apolipoprotein C-II and lipoprotein lipase at monomolecular lipid films

The triacylglycerol hydrolyase and phospholipase A 1 activities of bovine milk lipoprotein lipase toward long-chain fatty acyl ester substrates were investigated with monomolecular lipid films containing trioleoylglycerol and phosphatidylcholine. In a monolayer of egg phosphatidylcholine containing 3 mol% [ 14C]trioleoylglycerol, and in the presence of apolipoprotein C-II, a 79 amino acid activator protein for lipoprotein lipase, enzyme activity was maximal at a surface pressure of 21–22 mN · m −1 (37 μmol oleic acid released/h per mg enzyme); enzyme activity was enhanced 9-fold by apolipoprotein C-II. At surface pressures between 22 and 30 mN · m −1, lipoprotein lipase activity decreased over a broad range and was nearly zero at 30 mN · m −1. Apolipoprotein C-II and the synthetic fragments of the activator protein containing residues 56–79, 51–79 and 44–79 were equally effective at 20 mN · m -1 in enhancing lipoprotein lipase catalysis. However, at surface pressures between 25 and 29 mN · m −1, only apolipoprotein C-II and the phospholipid-associating fragment containing residues 44–79 enhanced enzyme catalysis. The effect of apolipoprotein C-II and synthetic peptides on the phospholipase A 1 activity of lipoprotein lipase was examined in sphingomyelin: cholesterol (2:1) monolayers containing 5 mol% di[ 14C]myristoylphosphatidylcholine. At 22 mN · m -1, apolipoprotein C-II and the synthetic fragments containing residues 44–79 or 56–79 enhanced lipoprotein lipase activity (70–80 nmol/h per mg enzyme). In contrast to trioleoylglycerol hydrolysis, the synthetic fragments were not as effective as apolipoprotein C-II in enhancing enzyme activity towards di[ 14C]myristoylphosphatidylcholine at higher surface pressures. We conclude that the minimal amino acid sequence of apolipoprotein C-II required for activation of lipoprotein lipase is dependent both on the lipid substrate and the packing density of the monolayer.

The covalent structure of apolipoprotein A-I from canine high density lipoproteins.

The complete amino acid sequence of apolipoprotein A-I (apo-A-I) from canine serum high density lipoproteins (HLD) has been determined by automated Edman degradation of the intact protein and proteolytic fragments derived therefrom. The major strategy involved analysis of overlapping sets of peptides generated by cleavage at lysyl residues with Myxobacter protease and by tryptic hydrolysis at arginines in the citraconylated protein derivative. Canine apo-A-I has 232 residues in its single polypeptide chain and its covalent structure is highly homologous to one of the two reported sequences for human apo-A-I. As in the case for the human apoprotein, predictive analysis of the canine apo-A-I sequence suggests that it comprises a series of amphiphilic alpha helices punctuated by a periodic array of prolyl residues. Human HDL contains a second major protein component, apolipoprotein A-II (apo-A-II) that is lacking in HDL from dog serum. The absence of apo-A-II in canine HDL raised the possibility that the apo-A-I from this source might contain within its primary structure sequences related to apo-A-II and thus perform the dual function of both proteins in one. Our analysis proves that canine apo-A-I has all of the structural features of human apo-A-I and that it is not an A-I: A-II hybrid molecule.