Biomedical subjects

J T Sparrow

Publications and source records attributed to J T Sparrow.

At least 19 recordsLinked to original sources

PubMed1992

Apolipoprotein E: phospholipid binding studies with synthetic peptides from the carboxyl terminus.

We have previously shown that the synthetic peptide apoE(129-169) forms lipid-peptide complexes with dimyristoylphosphatidylcholine (DMPC) with an L:P molar ratio of 125:1; the peptide in the isolated complex contains approximately 56% alpha-helicity. These results verify the presence of an amphipathic alpha-helix in this region of apoE as predicted by Chou-Fasman analysis and hydrophobicity calculations. To further define the lipid binding regions of apoE, we have synthesized four peptides, apoE(211-243), -(202-243), -(267-286), and -(263-286), from the carboxyl terminus of apoE and studied their lipid binding properties; apoE(202-243) contains two potential amphipathic helices. Although all four peptides formed alpha-helices in the helix-forming solvent 30% hexafluoropropanol, we found that only apoE(263-286) formed a stable complex with DMPC. The peptide contained approximately 80% alpha-helicity, and its Trp fluorescence spectrum was blue-shifted by 20 nm in the complex which had an L:P ratio of 163:1. We conclude that this sequence is a newly identified lipid binding region of apoE and that the amphipathic helices 203-221 and 226-243 are too hydrophilic to bind phospholipid.

Amino Acid Sequence↗

PubMed1992

Plasma lipid transport in the preruminant calf, Bos spp: primary structure of bovine apolipoprotein A-I.

The preruminant calf (Bos spp.) is a model of considerable interest with regard to hepatic and intestinal lipoprotein metabolism (Bauchart et al., J. Lipid Res. (1989) 30, 1499-1514 and Laplaud et al., J. Lipid Res. (1990) 31, 1781-1792). As a preliminary step towards future experiments dealing with HDL metabolism in the calf, we have purified apoA-I from this animal and determined its complete amino acid sequence. Thus, approx. 10% of calf apoA-I was shown to contain a propeptide, with the sequence Arg-His-Phe-Trp-Gln-Gln. Enzymatic cleavage of apoA-I resulted in 10 proteolytic peptides. The complete apoA-I sequence was obtained after alignment of peptides on the basis of their homologies with those from rabbit apoA-I. Thus calf apoA-I consists of 241 amino acid residues, and exhibits high sequence homology with all mammalian apoA-I's studied to date. The bovine protein contained 10 hydrophobic amphipathic helical regions, occurring between residues 43-64, 65-86, 87-97, 98-119, 120-141, 142-163, 164-184, 185-206, 207-217 and 218-241. A computer-constructed phylogenetic tree showed that bovine apoA-I was more closely related to its dog counterpart, including the presence of a single methionine, than to the corresponding macaque and human proteins. Comparative predictions of the respective antigenic structures of human and bovine apoA-I's using the Hopp-Woods algorithm indicated similar positions for all 13 detectable antigenic sites, among which 7 were of identical, or closely related, amino acid composition. This finding was confirmed by demonstration of partial immunological identity between the two proteins upon immunodiffusion analysis, a result obtained using a monospecific rabbit antiserum against bovine apoA-I. Finally, comparison of sequence homology between bovine apoA-I and the lecithin:cholesterol acyl transferase (LCAT) activating region of human apoC-I suggests that several LCAT activating domains may be present in calf apoA-I.

Amino Acid Sequence↗

PubMed1991

Synthesis of polyamide supports for use in peptide synthesis and as peptide-resin conjugates for antibody production.

We have synthesized beaded, hydrophilic cross-linked, aminoalkyl polydimethylacrylamide supports upon which peptides have been assembled using standard Boc or Fmoc chemistry in automated equipment. The resins were prepared by the free radical-initiated co-polymerization of N,N-dimethylacrylamide, N,N'-bisacrylyl-1,3-diaminopropane, and a functional monomer which were contained in a reverse-phase, detergent-emulsified suspension. The functional monomers used were N-(2-(methylsulfonyl)ethyloxycarbonyl)-allyl-amine (MSC-allylamine), N-acrylyl-1,6-diaminohexane hydrochloride or N-methacrylyl-1,3-diamino-propane hydrochloride. The MSC protecting group was removed by treatment of the resin with methanolic base during workup. After coupling of N-alpha-t-butyloxycarbonyl-alanine (Boc-alanine), amino acid analyses gave resin loading capacities between 0.15 mmol/g and 1.4 mmol/g, depending on the concentration and composition of the functional monomer. The resulting polymers were highly swollen by polar solvents including aqueous buffers. Peptides were synthesized on these supports after attaching the first amino acid directly or through a cleavable ester linker. When the carboxyl-terminal amino acid was coupled as the 4-oxymethylbenzoic acid derivative, the peptide could be deprotected and remain attached to the hydrophilic polymer since the peptide-benzyl ester bond was stable to HF deprotection at 0 degrees in the presence of 10% anisole and 1% ethanedithiol. The resulting peptidyl-resin could be swollen in aqueous buffers and injected into animals for the production of antibodies.

Acrylamides↗

PubMed1990

Dissociation of the stimulatory activities of staphylococcal enterotoxins for T cells and monocytes.

The staphylococcal enterotoxins (SEs) are homologous proteins related in their capacity for stimulating both T cells and monocytes. To assess the importance of conserved structure and sequence to functional activity, the role of the disulfide loop and adjacent sequence in these toxins was evaluated. Contrary to previous reports, we demonstrate here that the disulfide loop was required for the mitogenic activity of SEA and SEB. While T cell-stimulatory activity was compromised, reduced and alkylated SEs retained major histocompatibility complex class II-binding and monocyte-stimulatory activities, suggesting that their inability to induce T cell proliferation was due to failure to interact with T cell receptor (TCR) rather than with class II molecules. Reduction and alkylation did not affect the far-ultraviolet circular dichroic spectrum of SEA, suggesting that the loss of mitogenic activity was not associated with significant changes in secondary structure. The disulfide linkage imparts considerable stability to these toxins as peptide cleavages within the loop of SEB were not associated with detectable loss of function, although cleavage in the conserved sequence outside the loop of SEA resulted in loss of mitogenic activity. This report thus establishes a functional role for a conserved element in SEs, the disulfide loop, and further indicates that their class II- and TCR-binding activities can be dissociated.

Amino Acid Sequence↗

PubMed1990

Characterization and amino-terminal sequence of apolipoprotein AI from plasma high density lipoproteins in the preruminant calf, Bos spp.

The major apolipoprotein of calf plasma high-density lipoproteins, apo-AI, has been isolated and characterized. Apolipoprotein AI (apo-AI) was separated from the protein moiety of high-density lipoproteins (d 1.090-1.180 g/ml) by preparative electrophoresis in SDS-polyacrylamide gels followed by electrophoretic elution. Purified calf apo-AI had an Mr of approx. 27,000-28,000 in SDS-polyacrylamide gels, resembling human apo-AI. The amino acid composition of calf apo-AI displayed an overall similarity to that of its human and other mammalian counterparts (baboon, dog, badger, rabbit, rat and mouse), but differed in having higher proportions of glutamic acid, alanine and isoleucine. Amino-terminal amino acid sequence analysis up to the 47th residue showed close homology between calf apo-AI and those of the mammals with which it was compared. However, residues 2, 7, 20 and 22 in calf AI (i.e. aspartic acid, serine, glutamic acid and isoleucine, respectively) were substituted by glutamic acid, proline or glutamine, aspartic acid, and valine or leucine respectively, in the other mammals.

Age Factors↗

PubMed1990

Crystallization and preliminary x-ray diffraction study of synthetic apolipoprotein E fragment (residues 129-169).

Apolipoprotein E is a plasma protein comprised of a lipid binding region (which together with other apoproteins maintains the structure of lipoprotein particles) and a receptor binding domain (which interacts with cellular receptors for control of triglyceride and cholesterol metabolism). A peptide, comprising residues 129-169 of human apolipoprotein E, which contains both a putative lipid-binding region and receptor binding domain, has been synthesized by solid phase techniques. Diffraction quality crystals of the synthetic apolipoprotein E fragment129-169 have been obtained at room temperature by vapor diffusion with polyethylene glycol in the presence of the nonionic detergent beta-octylglucoside. The crystals have been characterized with x-radiation as orthorhombic, space group I222 or I2(1)2(1)2(1), with unit cell dimensions a = 61.91, b = 30.84, and c = 42.79 A. There are eight molecules per unit cell, with one molecule (Mr = 4771) in each asymmetric unit. Precession photographs show that crystals diffract beyond 2.7-A resolution and are stable in the x-ray beam at room temperature for at least 200 h; thus, they can be used to collect three-dimensional data for a detailed crystallographic analysis.

Apolipoproteins E↗

PubMed1989

Interaction of glycosaminoglycans with lipoproteins.

Apolipoproteins B-100 and E are protein constituents of human plasma chylomicrons, very low (VLDL), and low density lipoproteins (LDL). The interaction of lipoproteins with cell receptors is mediated by apoB and E. Lipoproteins also bind to the extracellular matrix, such as glycosaminoglycans (GAG), forming insoluble complexes in the presence of Ca2+. The purpose of this study was to identify the GAG-binding domains in apoB and E. By a combination of fragmentation of the intact proteins, peptide synthesis and quantitative GAG-binding, domains in apoB and apoE were identified and are shown below. These domains contain clusters of basic amino acids that we suggest are required for GAG-binding. table; see text.

Amino Acid Sequence↗

PubMed1988

Kinetics and mechanism of transfer of synthetic model apolipoproteins.

The effect of hydrophobicity on the rate and mechanism of transfer of a synthetic amphiphilic peptide between phosphatidylcholine single bilayer vesicles has been evaluated. These peptides, which had the sequence Cn-SSLKEYWSSLKESFS (where Cn represents a saturated acyl chain of n carbons that is attached to the amino terminus of the peptide and n = 8, 12, or 16), were distinguished by the length of the saturated acyl chain of n carbons that was covalently bonded to the amino terminus. The transfer of the peptides was monitored by following the rate of change of the intrinsic tryptophan fluorescence that followed mixing of donor vesicles, which contained peptide, phosphatidylcholine, and a fluorescence quencher, with acceptors composed only of phosphatidylcholine. The transfer rates were independent of the structure and concentration of the acceptor. The kinetics were biexponential with the contribution of the fast and slow components being nearly equal. The rates of both components decreased with increasing acyl chain length; the respective free energies of activation were linear with respect to the acyl chain length. These results showed that, unlike lipid transfer, peptide transfer is not always a simple unimolecular process. However, like lipid transfer, the transfer rates are a predictable function of hydrophobicity. It is proposed that the peptides exist as dimers on the phospholipid surface and that the two components of transfer are due to sequential transfer of each molecule in a dimer.

Amino Acid Sequence↗

PubMed1988

Primary sequence mapping of human apolipoprotein B-100 epitopes. Comparisons of trypsin accessibility and immunoreactivity and implication for apoB conformation.

Differential trypsin-accessibility and monoclonal antibodies (Mabs) to human apolipoprotein (apo) B-100 are both important tools for probing apoB structure and conformation on low-density lipoproteins (LDL). In this study, we have mapped greater than 80% of the C-terminal region (720 residues) of LDL apoB-100 using trypsin digestion. Our results extend our previous data [Yang et al. (1986) Nature (Lond.) 323, 738-742] confirming that the C-terminal region of about 420 residues of apoB-100 is largely inaccessible to trypsin, whereas the part just preceding this region has interspersed trypsin-accessible and inaccessible peptides. We have determined the amino acid sequence of specific apoB-100 peptides containing epitopes recognized by four separate Mabs: two epitopes have been mapped to within 20 residues, one has been mapped to 36 residues, and the last to 80 residues. We used polyclonal antisera to identify 16 overlapping clones of varying lengths of apoB-100 cDNAs extending from the C-terminus of apoB-100 cloned in the expression vector, lambda gt11. These clones were then tested against individual Mabs. By nucleotide sequence analysis of overlapping clones that show differential reactivities to different Mabs, we have mapped the individual epitopes of each Mab to within about 50-150 amino acid residues predicted from the DNA sequences. Confirmation and further fine mapping were accomplished by competition for LDL binding using partially purified fusion proteins and chemically synthesized oligopeptides. Two epitopes (Mabs 7 and 22) were mapped to the C-terminal 20 amino acids of apoB-100, one (Mab 16) to residues 4154-4189, and another (Mab 20) to residues 3926-4005. Mab 16 precipitates more than 80% of LDL particles. Mab 20 precipitates only denatured apoB but not native LDL apoB [Milne et al. (1987) Mol. Immunol. 24, 435]. Mabs 7 and 22 are unique in that they precipitate LDL apoB modified by storage much better than freshly isolated LDL-apoB. Although epitope expression and trypsin-accessibility represent two useful probes for the study of protein conformation, there was no obvious correlation between these two parameters when applied to LDL apoB for the antibodies we have examined.

Amino Acid Sequence↗

PubMed1987

Monoclonal antibodies as probes of high-density lipoprotein structure: identification and localization of a lipid-dependent epitope.

Eight stable murine monoclonal antibodies (mabs) were raised against human high-density lipoproteins (HDL). Three different antibody reactivities were demonstrated by immunoblotting. A group of five antibodies were specific for apolipoprotein A-I (apoA-I) and bound to similar or overlapping epitopes. The second type of reactivity, shown by mab-32, was specific for apoA-II. In the third group, two antibodies showed high reactivity with apoA-II and slight cross-reactivity with apoA-I. The properties of two antibodies, mab M-30 specific for apoA-I and mab M-32 specific for apoAII, were characterized in detail as probes of HDL structure. The association of 125I-labeled HDL or synthetic complexes of apoA-I and phosphatidylcholine with mab M-30 was lipid dependent. Mab M-32 binding to apoA-II was independent of lipid. The lipid-dependent epitope bound by mab M-30 has been localized to an 18 amino acid synthetic apoA-I peptide. Moreover, studies with HDL2, HDL3, and immunoadsorbed HDL subfractions indicate that binding of mab M-30 to HDL is influenced by some component within the microenvironment individual HDL particles. These lines of evidence suggest that the molar ratio of apoA-I to apoA-II is the critical determinant. Binding of mab M-32 to HDL increased the reactivity of HDL to mab M-30 in a dose-dependent manner, indicating an unusual form of cooperativity between two mabs that recognize different proteins in HDL. These monoclonal antibodies will be valuable in studies of the metabolic significance of protein-protein and lipid-protein interactions in HDL.

Animals↗

PubMed1987

Use of a resin-bound synthetic peptide for identifying a neutralizing antigenic determinant associated with the human immunodeficiency virus envelope.

A polyamide-based solid-phase support containing an acid-stable p-(oxymethyl)benzoic acid handle to anchor the COOH-terminal amino acid was utilized in the production of synthetic peptides analogous to amino acid sequences 503-532 from the human immunodeficiency virus (HIV) envelope glycoprotein. The resin-bound peptide was used to induce an antibody response to the native form of glycoprotein 120 in both rabbits and mice. This epitope was detected on the surface of HIV-infected cells and was capable of inducing an in vitro neutralizing HIV antibody response. In addition, sera from some individuals exposed to HIV react with this peptide bound to the resin in a solid-phase immunoassay. These data indicate that we have identified a neutralizing antigenic determinant present on the amino-terminal glycoprotein 120 subunits of HIV by utilizing resin-bound synthetic peptides.

Acquired Immunodeficiency Syndrome↗

PubMed1987

Dihydrotestosterone heptanoate: synthesis, pharmacokinetics, and effects on hypothalamic-pituitary-testicular function.

Dihydrotestosterone heptanoate (DHT-hp), a seven-carbon fatty acid ester of DHT, was synthesized, and its pharmacokinetics and effects on hypothalamic-pituitary-testicular function were determined in men and pubertal boys. Plasma DHT levels markedly increased 24 h after im injection of DHT-hp, reached their peak during the first week, and fell to baseline levels after 4-6 weeks. An estimated 43-55% of DHT-hp was converted to DHT 4-6 weeks after injection. Plasma testosterone, estradiol, LH, and FSH levels decreased by 4 days after DHT-hp injection, were lowest during the second week, and returned to baseline values after 4-6 weeks. The LH and FSH responses to GnRH were diminished by chronic administration of DHT-hp to pubertal boys at 3-week intervals for 15 weeks. The affinity of DHT-hp was 100 times less than the affinity of DHT for the human androgen receptor, and no affinity for the estrogen receptor in breast tissue could be demonstrated. Since DHT is a nonaromatizable androgen, and neither DHT nor DHT-hp binds readily to the estrogen receptor, suppression of LH and FSH secretion by this drug probably occurs via an androgen-dependent mechanism. Receptor binding and pharmacokinetic data indicate that unesterified DHT is the active principle. DHT-hp is a useful derivative of DHT, since prompt, predictable, and sustained rises in DHT occur after its administration.

Adult↗

PubMed1986

Determination of the molecular mass of apolipoprotein B-100. A chemical approach.

Apolipoprotein B-100 (apo B-100) is the protein ligand in low-density lipoproteins that binds to a specific cell-surface receptor. Its molecular mass has been a subject of controversy. We have determined the molecular mass of the protein by a chemical approach. After complete CNBr cleavage, the C-terminal fragment of apo B-100 was purified by reverse-phase h.p.l.c. Amino acid N- and C-terminal analyses confirm that this peptide represents the C-terminal peptide as deduced from the DNA sequence of a human apo B-100 cDNA clone. A chemically synthesized peptide was used to determine the recovery of the peptide (74.72%). On the basis of these data, the molecular mass of apo B-100 was determined to be 496.82 +/- 24.84 kDa.

Amino Acid Sequence↗

PubMed1986

Apolipoprotein C-III/sphingomyelin recombinants: formation, isolation, and characterization.

The association of apolipoprotein C-III (apoC-III) from human very low density lipoprotein with sphingomyelin from egg yolk (EYSM) has been studied at the transition temperature (Tc) of the phospholipid. Upon incubation of aliquots of the apoprotein with increasing amounts of sphingomyelin, the alpha-helical content of the apoprotein increased from 20% in the absence of EYSM to a limiting value of 67% at a protein:lipid molar ratio of 1:200. The tryptophan fluorescence spectrum of the apoprotein exhibited a gradual blue shift from 356 nm in the absence of EYSM to 348 nm when the protein:lipid ratio in the complex had reached 1:50. Gel filtration chromatography of complexes formed by incubating the apoprotein and phospholipid at differing apoC-III:EYSM ratios demonstrated a disintegration of sphingomyelin vesicles into particles of decreasing size with increasing proportion of protein. This effect was confirmed by sedimentation velocity experiments in which the observed sedimentation coefficient of EYSM decreased from 14.0 S (for vesicles) to a limiting value of 7.0 S when the apoprotein:phospholipid ratio reached 1:50 in the complex. Electron micrographs of negatively stained EYSM vesicles showed spherical particles of 380-A diameter. Addition of apoC-III led to the formation of disk-shaped structures whose diameter decreased to a limiting value of 204 +/- 34 A at a protein:lipid ratio of 1:50. In contrast, the disk thickness was relatively constant at 51 +/- 2 A for all isolated complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein C-III↗

PubMed1986

Human lysosomal sphingomyelinase: substrate efficacy of apolipoprotein/sphingomyelin complexes.

Human apolipoprotein stimulation of sphingomyelin (SM) hydrolysis by sphingomyelinase from human skin fibroblasts has been studied. Apolipoproteins A-I, A-II, B, C-I, and E do not enhance sphingomyelin hydrolysis above control levels. In contrast, apoC-II stimulates sphingomyelin hydrolysis by approximately 2.5-fold. ApoC-III, the most potent apoprotein activator, stimulates hydrolysis by 3-4-fold. ApoC-III stimulation is not significantly different for the three different isoforms which carry 0, 1, or 2 sialic acid residues. The amino-terminal half of this apoprotein, C-III(1-40), which does not bind to phospholipid surfaces, does not activate sphingomyelinase. In contrast, the carboxyl-terminal half, C-III(41-79), which strongly binds to phospholipid surfaces, stimulates sphingomyelin hydrolysis to the same level as that produced by the intact, full-length apoprotein. Incubation of sphingomyelin vesicles with increasing proportions of apoC-III results in the formation of complexes of increasing apoC-III:SM ratio and decreasing radius. The hydrolysis of sphingomyelin in the 1:50 (mol/mol) complex was more than 2-fold greater than that of the 1:200 (mol/mol) complex. The rate of hydrolysis of egg yolk sphingomyelin in the 1:50 complex was maximal [0.9 mumol h-1 (mg of protein)-1] at the gel----liquid-crystalline phase transition temperature (Tm) of the complex (40 degrees C). The rate of hydrolysis fell markedly at either higher or lower temperature. Determination of the apparent Km and Vmax values below, at, and above Tm indicated that the temperature dependence of sphingomyelin hydrolysis was attributable primarily to changes in Vmax.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein C-III↗

PubMed1986

Lipid-peptide association and activation of lecithin:cholesterol acyltransferase. Effect of alpha-helicity.

A series of apolipopeptides, in which single proline substitutions were made at various sites in the 20-residue sequence, have been synthesized and tested. These peptides have nearly the same hydrophobic content, but very different helical contents, in a structure-making solvent. The affinity of these peptides for phospholipids was evaluated on the basis of their intrinsic tryptophan fluorescence and equilibrium dialysis against model high density lipoproteins. Proline substitutions at one end of the peptide had little or no effect on the fluorescence, circular dichroism, affinity for model high density lipoproteins, or activation of human plasma lecithin:cholesterol acyltransferase. By contrast, there was a dramatic change in all of these variables as the site of substitution was moved progressively closer to the middle of the peptide. All of these data suggested that a helix breaker that is substituted at the midpoint of a helical surface-associating peptide will greatly reduce its affinity for phospholipid surfaces. These results demonstrate that helicity and hydrophobicity are independent determinants of the affinity of an apolipopeptide for a phospholipid surface.

Amino Acid Sequence↗

PubMed1986

Human apolipoprotein E. Determination of the heparin binding sites of apolipoprotein E3.

The interaction of human apolipoprotein (apo-) E3 with heparin was examined using heparin-Sepharose as a model system. The approach taken to determine the region of apo-E that is responsible for binding to heparin was to identify apo-E monoclonal antibodies that inhibited heparin binding, to determine the epitopes of the inhibiting antibodies, and finally to examine the heparin binding of fragments containing the inhibiting antibody epitopes. Three antibodies, designated 1D7, 6C5, and 3H1, were found to inhibit binding, suggesting that multiple heparin binding sites were present on apo-E. The epitopes of the inhibiting antibodies were determined by immunoblot analysis of synthetic or proteolytic fragments of apo-E. Measurement of the heparin binding activity of fragments containing epitopes of the inhibiting antibodies demonstrated that apo-E3 contains two heparin binding sites. The first site is located in the vicinity of residues 142-147 and coincides with the 1D7 epitope. The second binding site is contained in the carboxyl-terminal region of apo-E and is inhibited by 3H1, the epitope of which is located between residues 243 and 272. The epitope of the third inhibiting antibody, 6C5, is located at the amino terminus of apo-E; however, this antibody inhibits the second heparin binding site located in the carboxyl-terminal region. A head-to-tail association of apo-E, in which the 6C5 epitope and the second heparin binding site would be in close proximity, is proposed to account for this observation. In the lipid-free state both heparin binding sites on apo-E are expressed; however, when apo-E is complexed to phospholipid or on the surface of a lipoprotein particle, only the first binding site (residues 142-147) is expressed.

Animals↗

PubMed1986

Binding of a high reactive heparin to human apolipoprotein E: identification of two heparin-binding domains.

Ligand-blotting and dot-blotting procedures were used to investigate the binding of [125I]-heparin to apolipoprotein E, its thrombin fragments E22 (residues 1-191) and E12 (residues 192-299), and to nine apolipoprotein E synthetic fragments. E22 and E12 bound [125I] heparin indicating multiple heparin-binding domains. Synthetic peptides of apoE corresponding to residues 129-169, 139-169, and 144-169, but not 148-169, bound [125I] heparin suggesting that residues 144-147 (Leu-Arg-Lys-Arg) in E22 are important for binding. Peptide 202-243 and 211-243 but not 219-243 bound [125I] heparin suggesting that residues 211-218 (Gly-Glu-Arg-Leu-Arg-Ala-Arg-Met) comprise a portion of the E12 heparin-binding domain.

Amino Acid Sequence↗