Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.1.34 (lipoprotein lipase)
 7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In order to determine the role of apoprotein (apo) B conformation in the activation of the lysolecithin acyl-transferase reaction, we studied the activation of purified enzyme by various subfractions of low density lipoprotein (LDL), isolated by density gradient centrifugation. The activation of LAT correlated positively with the density of LDL and negatively with cholesterol/protein and triglyceride (TG)/protein ratios. The enzyme activation was also positively correlated with the number of trinitrobenzenesulfonic acid-reactive lysine amino groups, which increased with increasing density of LDL. The immunoaffinity of the LDL subfractions for B1B6, a monoclonal antibody directed to the receptor-binding region of apoB, increased with increasing density, while the affinity toward C1.4, a monoclonal antibody directed to the amino-terminal region of apoB, was not altered. Enrichment of normal whole LDL with TG resulted in a 45% reduction in enzyme activation, a 27% decrease in the number of trinitrobenzenesulfonic acid-reactive lysine groups, and a marked reduction in the immunoaffinity for B1B6. All these parameters reversed to normal when the TG-enriched LDL was treated with milk lipoprotein lipase, which specifically reduced the TG content of LDL. The LDL subfractions also supported cholesterol esterification by the purified enzyme, in parallel with lysolecithin esterification, indicating that apoB can also serve as an activator of the lecithin-cholesterol acyltransferase reaction. These results strongly suggest that the localized conformational change of apoB which occurs during the TG depletion of the precursor particle is critical for its activation of acyltransferase reactions, in a manner analogous to its interaction with the cellular receptors.
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PMID:Effect of apoprotein B conformation on the activation of lysolecithin acyltransferase and lecithin: cholesterol acyltransferase. Studies with subfractions of low density lipoproteins. 154 96

The relationship between maturation of lipoprotein lipase (LPL) and its translocation from the endoplasmic reticulum (ER) to the Golgi complex was determined by measuring lipolytic activity under conditions preventing transport of the enzyme from the ER to the Golgi compartment. In the presence of brefeldin A, a reagent that inhibits movement of proteins from the ER and causes the disassembly of the Golgi complex, pro-5 Chinese hamster ovary cells accumulated catalytically active LPL, while secretion of the enzyme was effectively blocked. LPL retained intracellularly by brefeldin A treatment possessed oligosaccharide chains that were processed to the complex form by the Golgi enzymes redistributed into the ER. At 16 degrees C, a condition disrupting protein transport to the cis-Golgi, the retained enzyme again remained catalytically active although the oligosaccharides remained in the high mannose form. Lastly, attachment of the specific ER retention signal KDEL (Lys-Asp-Glu-Leu) to the carboxyl terminus of LPL also resulted in intracellularly retained enzyme that was fully active. The importance of oligosaccharide processing for attainment of LPL catalytic activity in vitro was also determined. LPL was active and secreted when trimming of the mannose residues was inhibited by deoxymannojirimycin and when addition of complex sugars was blocked using Chinese hamster ovary mutants (lec1 and lec2), indicating that these processing events are not necessary for the expression of a functional enzyme. However, blocking glucose removal by glucosidase inhibitors (castanospermine and N-methyl-deoxynojirimycin) resulted in a significant reduction in LPL specific activity and secretion. Thus, glucose trimming of LPL oligosaccharides is essential for enzyme activation; however, further oligosaccharide processing or translocation of the enzyme to the cis-Golgi is not required for full expression of lipolytic activity in vitro.
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PMID:Maturation of lipoprotein lipase. Expression of full catalytic activity requires glucose trimming but not translocation to the cis-Golgi compartment. 155 30

Two major isoforms of the bovine analogue to human apolipoprotein (apo) CII were purified from plasma. They were both as effective as human apo CII in activating lipoprotein lipase. Amino acid sequencing revealed that one form contained 79 amino acid residues, and corresponded to human pro apo CII. The other form lacked the first six residues at its N-terminus. This was apparently due to cleavage of the -Gln-Asp- linkage in the sequence H2N-Ala-His-Val-Pro-Gln-Gln-Asp-Glu-, analogous to cleavages described for human apo AI and apo CII. Previous studies with human apo CII have shown that the ability to activate lipoprotein lipase resides in the C-terminal third of the molecule. This was highly conserved in the bovine analogue: of the 30 last residues, 21 are identical. Five residues in this part of human apo CII have been reported to be essential for activation of lipoprotein lipase. Only one of these, Tyr63, is present in the bovine sequence. The bovine structure contains a threonine at position 61, instead of serine in the human, and the four last residues are -Ser-Gly-Lys-Asp instead of the allegedly necessary -Lys-Gly-Glu-Glu. Three differently sialylated isoforms of the bovine analogue to human apolipoprotein CIII were also isolated and partially sequenced. All three lacked the first three N-terminal residues as compared to sequences from other species (man, dog and rat). Sequence differences were more pronounced at the ends than in the central parts of the apo CIII molecules.
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PMID:Primary structure of the bovine analogues to human apolipoproteins CII and CIII. Studies on isoforms and evidence for proteolytic processing. 220 8

In this study we have prepared peptides of the C-terminal domain of apolipoprotein CII (ApoCII) by a solid-peptide-synthesis technique and demonstrated that the C-terminal tetrapeptide, Lys-Gly-Glu-Glu, represents an inhibitor of lipoprotein lipase. The tetrapeptide not only inhibits the basal activity of lipoprotein lipase, but also blocks the activation effect of native ApoCII. The lengthening of this tetrapeptide resulted in a corresponding increase in affinity for lipoprotein lipase. This suggested that amino acids other than those of the C-terminal tetrapeptide also contribute to the binding affinity of ApoCII for lipoprotein lipase. On the basis of an essential requirement of the ApoCII terminal domain for binding to lipoprotein lipase, we suggest that the initial interaction of ApoCII, mediated via the C-terminal tetrapeptide, promotes the proper alignment of ApoCII with lipoprotein lipase, followed by the weak interaction of the ApoCII activator domain with the lipoprotein lipase activator site, enhancing the lipolysis process.
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PMID:C-terminal domain of apolipoprotein CII as both activator and competitive inhibitor of lipoprotein lipase. 238 83

The primary structure of bovine milk lipoprotein lipase (bLPL) was determined by alignment of peptides produced by tryptic digestion, Staphylococcus aureus V8 protease digestion, and cyanogen bromide cleavage. bLPL consists of 450 amino acid residues. Most tryptic peptides were isolated and analyzed, except for the dipeptide, Glu-Lys (position 423-424), and the 2 Lys at positions 416 and 488. Peptides resulting from digestion by S. aureus V8 protease and cyanogen bromide cleavage filled the missing part and completed the primary sequence of bLPL. The NH2 terminus of bLPL was determined to be Asp by sequencing the intact protein with a gas phase sequencer for up to 30 residues, whereas the COOH terminus was identified as Gly through, carboxyl peptidase Y cleavage. The enzyme contains 10 cysteine residues, all of which exist in disulfide linkages. They are formed between Cys29 and Cys42, Cys218 and Cys241, Cys266 and Cys285, Cys277, and Cys280, and Cys420 and Cys440. The sites of N-glycosylation were identified at Asn44 and Asn361. In accordance with a common structural homology of serine-type esterases, -G-X-S-X-G- (Yang, C. Y., Manoogian, D., Pao, Q., Lee, F., Knapp, R. D., Gotto, A. M., Jr., and Pownall, H. J. (1987) J. Biol. Chem., 262, 3086-3191), the active site serine of bLPL was assigned to the serine at position 134. The chymotrypsin nick of bLPL was determined to be between residues 390 and 391. A model of the enzyme is proposed on the basis of our data and available chemical data.
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PMID:Structure of bovine milk lipoprotein lipase. 267 42

Bovine milk lipoprotein lipase was subjected to amino acid sequence analysis. The first 19 amino-terminal residues were Asp-Arg-Ile-Thr-Gly-Gly-Lys-Asp-Phe-Arg-Asp-Ile-Glu-Ser-Lys-Phe-Ala-Leu- Arg. In addition, reversed-phase high-performance liquid chromatography of a tryptic digest of reduced and alkylated lipase resolved a number of peptides, five of which contained cysteine. Sequence analysis of the tryptic peptides revealed in most instances a close homology to porcine pancreatic lipase. Based on this homology, the relative alignment of the sequenced lipoprotein lipase peptides can be made. In addition, a potential binding site for the triacylglycerol substrate and a carbohydrate-binding domain for lipoprotein lipase are postulated.
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PMID:Homology of lipoprotein lipase to pancreatic lipase. 345 70

Lipoprotein lipase from bovine milk reacted stoichiometrically with diisopropylphosphorofluoridate (DFP), an inactivator of serine esterases, resulting in the loss of enzymatic activity against triacylglycerols. The reaction obeyed first-order kinetics with a rate constant of 0.69 h-1. In order to isolate the peptide containing the diisopropylphosphoryl moiety (DIP), partially purified lipoprotein lipase was covalently labeled with [3H]DFP, and the labeled protein was reduced, carboxymethylated, and further purified to about 90% homogeneity. Cyanogen bromide cleavage followed by gel filtration yielded a radioactive peptide of 6-8 kDa. This peptide was succinylated and then digested with Staphylococcus aureus V8 proteinase. From this digest, a peptide containing 0.95 mol of [3H] DIP/mol of peptide was isolated by gel-permeation chromatography followed by reverse-phase high performance liquid chromatography. Automated Edman degradation provided the following sequence: Ala-Ile-Gly-Ile-His-Trp-Gly-Gly- (DIP)Ser-Pro-Asn-Gln-Lys-Asn-Gly-Ala-Val-Phe-Ile-Asn-(Ser, Leu)-Glu. Analysis of the sequence for secondary structure suggests that the reactive serine of lipoprotein lipase is in a beta-turn, a structure similar to those of the active sites of most other serine proteinases. Lipoprotein lipase appears to share this secondary structure with other serine hydrolases despite significant differences in the primary structure of this domain.
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PMID:Isolation of an active-site peptide of lipoprotein lipase from bovine milk and determination of its amino acid sequence. 352 32

Lipoprotein lipase activity was measured in an acetone-dried-powder preparation from rat epididymal adipose tissue using pig serum or pig serum lipoprotein, which had been chemically modified, as activator. Modification of acidic amino acids of lipoproteins with NN-dimethyl-1,3-diamine resulted in a complete loss of ability to activate lipoprotein lipase. Modification of 34% of lipoprotein arginine groups with cyclohexanedione resulted in the loss of 75% of the activation of lipoprotein lipase; approx. 42% of the original activity was recovered after reversal of the modification. This effect was dependent on the cyclohexanedione concentration. Modification of 48% of lipoprotein lysine groups with malonaldehyde decreased the maximum activation by 20%, but three times as much lipoprotein was required to achieve this. Non-enzymic glycosylation of lipoprotein with glucose, under a variety of conditions resulting in up to 28 nmol of glucose/mg of protein, had no effect upon the ability to activate lipoprotein lipase. In contrast non-enzymic sialylation resulted in a time-dependent loss of up to 60% of ability to activate lipoprotein lipase. Reductive methylation and acetoacetylation of serum did not affect the ability to activate lipoprotein lipase. The results are compared to the effects of similar modifications to low density lipoproteins on receptor-mediated endocytosis.
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PMID:The effects of chemically modifying serum apolipoproteins on their ability to activate lipoprotein lipase. 359 62

We have isolated an isoform of the protein activator of lipoprotein lipase, apolipoprotein C-II, from the very low density lipoproteins of four patients of African ancestry with hypertriglyceridemia and eruptive or pedunculated xanthomata. This protein, which we designate apolipoprotein C-II2, differs from the previously recognized species, which we denote apolipoprotein C-II1, by substitution of glutamine for lysine at residue 55, a mutation which would require only a single-base substitution in the structural gene for apolipoprotein C-II1. Each of the patients in whom apolipoprotein C-II2 was found had approximately equal amounts of apolipoprotein C-II1 and apolipoprotein C-II2 among the apoproteins of the very low density lipoproteins, suggesting that the structural genes for these proteins are allelic. Two additional apparent heterozygotes were found among the first-degree relatives of each of two of the patients in patterns compatible with monogenic autosomal transmission. Approximately equal amounts of apolipoproteins C-II2 and C-II1 were also found by isoelectric focusing in 6 of a casual series of 50 normolipidemic blacks, but none or only trace amounts of apolipoprotein C-II2 were found in 500 samples from Caucasian subjects with hyperlipidemia. These findings suggest that this polymorphism is distributed primarily among blacks, possibly reflecting some positive Darwinian selection pressure. Whether this polymorphism has a modifying effect upon the development of hyperlipemia remains to be determined.
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PMID:A variant primary structure of apolipoprotein C-II in individuals of African descent. 394 71

The molecular models of two microbial lipases and human pancreatic lipase (PL) have suggested the existence of common structural motifs including a buried active site shielded by an amphipathic surface loop. In an effort to explore the role of residues comprising the loop of lipoprotein lipase (LPL), we have used site-directed mutagenesis to generate three new LPL variants. In variant LPLM1 we deleted 18 amino acids leaving a loop of only 4 residues which resulted in an LPL protein inactive against triolein substrates. In contrast, two other LPL variants with only partial deletions, involving the apical section of the loop [LPLM2 (-8 amino acids) and LPLM3 (-2 amino acids)] manifested normal lipolytic activity. These findings indicate a critical requirement for the maintenance of charge and periodicity in the proximal and distal segments of the LPL loop in normal catalytic function. This is further highlighted by the detection of a mutation in the proximal section of the loop in a patient with LPL deficiency at position 225 which results in a substitution of threonine for isoleucine. The intact catalytic activity of the partial deletion variants (LPLM2 and LPLM3) further suggests that the apical residues of the loop contribute minimally to the functional motifs of the active site. We support this postulate by showing that the conserved glycine in the apical turn section (G229) can be substituted by glutamine, lysine, proline, or threonine without significantly affecting catalytic activity.
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PMID:Structure-function relationships of lipoprotein lipase: mutation analysis and mutagenesis of the loop region. 822 42


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