Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P02749 (beta2-glycoprotein I)
 836 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Isoelectric focusing of purified beta 2-glycoprotein I (beta 2-G-I) revealed five major bands with isoelectric points (pI) between 5.1 and 6.1. Neuraminidase treatment decreased the number of bands to two (pI 8.0 and 8.2). The two asialo subfractions of beta 2-G-I were purified by cation-exchange column chromatography. The more basic isoform II was found to have a higher content of lysine. Western-blot analysis of different plasma samples confirmed the heterogeneity of beta 2-G-I in plasma. Plasma treated with neuraminidase showed two bands irrespective of the number of isoforms as well as of the concentration in native plasma. This led us to the conclusion that human plasma beta 2-G-I consists of two isoproteins that are sialylated to different extents.
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PMID:Characterization of isoelectric subspecies of asialo-beta 2-glycoprotein I. 276 87

beta 2-Glycoprotein I-cardiolipin complexes are reported to be a target antigen for the binding of a subset of anti-phospholipid antibodies. The characteristics of binding of beta 2-glycoprotein I to cardiolipin are reported in this paper. Binding at neutral pH is specific, saturable, dependent on ionic strength and independent of bivalent cation. Binding at low pH is qualitatively different from that at neutral pH, and is not dependent on ionic strength. Denaturation of beta 2-glycoprotein I by heat inactivation and reduction/alkylation indicates that beta 2-glycoprotein I-cardiolipin interaction does not require the native three-dimensional structure of beta 2-glycoprotein I, implying that a linear sequence motif may be responsible. Modification of amino acid residues by KCNO treatment completely destroys binding capacity, indicating crucial involvement of lysine residues in binding of beta 2-glycoprotein I to cardiolipin. Complement factor H, which has some similar highly charged linear sequence motifs to beta 2-glycoprotein I and is composed of the same type of protein module, was found to bind to cardiolipin and inhibit the binding of beta 2-glycoprotein I to cardiolipin. Three different lysine-rich segments of the fifth domain of beta 2-glycoprotein I may be involved in binding to cardiolipin.
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PMID:Characterization of binding of human beta 2-glycoprotein I to cardiolipin. 764 62

Using recombinant (r)HBsAg as a ligand, we previously found a 46-kDa human plasma protein capable of specific binding, and identified this protein as apolipoprotein H (apo H). Apo H is able to bind to rHBsAg containing only the small S protein, in both ligand blot and enzyme immunoassay systems (H. Mehdi, M.J. Kaplan, F.Y. Anlar, X. Yang, R. Bayer, K. Sutherland, and M.E. Peeples, J. Virol. 68, 2415-2424, 1994). Apo H is a plasma glycoprotein, some of which is associated with lipoproteins, particularly chylomicrons and high-density lipoproteins (HDL). During normal lipid trafficking in the bloodstream, chylomicrons and HDL are targeted to the hepatocyte, the primary host cell for HBV, for degradation. In this report the method of apo H presentation was examined. rHBsAg bound to apo H very poorly if the apo H was coated directly on a microtiter well, or if it was presented in a soluble form. Binding was 100-fold more efficient when apo H was presented as a complex with monoclonal antibody (MAb) P2D4. These results suggest that binding to this MAb alters apo H, making it highly reactive with rHBsAg. Apo H binding to rHBsAg is not dependent on divalent cations and is optimal at pH 6.5-8.0. Removal of lipids from rHBsAg resulted in denaturation, preventing analysis of binding activity. Removal of sialic acid or complete removal of N-linked carbohydrates from apo H did not change its ability to bind rHBsAg, indicating that apo H carbohydrates are not involved in rHBsAg binding. Likewise, chemical modification of the arginine residues of apo H had no effect on binding. However, chemical modification of as few as three of the 29 lysine residues of apo H destroyed binding, indicating that one or a few lysines in apo H are involved in rHBsAg binding.
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PMID:An altered form of apolipoprotein H binds hepatitis B virus surface antigen most efficiently. 859 36

This study has been undertaken to assess whether anticardiolipin and anti-beta 2-GPI are two distinct populations of (auto)antibodies, and to clarify whether the beta 2-GPI region critical for phospholipid binding is also crucial for anti-beta 2-GPI reactivity. Fourteen of the 62 anticardiolipin (aCL) ELISA positive sera (22.6%) were positive for anti-beta 2-GPI by immunoblotting, 42 (67.7%) for aCL using TLC immunostaining. IgG fractions from 5 sera gave the same anticardiolipin reactivity detected by TLC immunostaining in the corresponding sera. All anti-beta 2-GPI-positive sera were reactive with the phenylthiocarbamyl derivative of the protein, indicating that binding of phenylisothiocyanate with lysine residues does not modify the molecule antigenicity. In addition, incubation of IgG fractions with the phospholipid binding site did not modify reactivity with beta 2-GPI. These findings demonstrate that: a) "true" antiphospholipid antibodies are detectable in patients' sera; b) aCL and anti-beta 2-GPI have a different immunological profile; c) the beta 2-GPI phospholipid-binding site is not the region recognized by the antibodies.
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PMID:Anticardiolipin and anti-beta 2-GPI are two distinct populations of autoantibodies. 881 81

Increased nonenzymatic glycosylation of all major classes of apolipoproteins has been demonstrated in diabetes. In this work we deal with the in vitro nonenzymatic glycosylation of apolipoprotein H, whose role in lipid metabolism is still poorly understood and whose levels increase in diabetes. Apolipoprotein H was isolated from human plasma and purified through a combination of affinity chromatography and continuous elution electrophoresis. The in vitro glycosylation was performed by incubating purified apolipoprotein H with high concentration of glucose. Our results indicate that the in vitro nonenzymatic glycosylation has no effect on the physical properties of apolipoprotein H, despite the fact that this apolipoprotein contains a high number of lysine residues. Since the in vitro concentration of glucose was far higher than the levels normally found in diabetic subjects, it is unlikely for apolipoprotein H to become glycosylated in diabetes.
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PMID:Apolipoprotein H is not affected by in vitro glycosylation. 1033 90

Apolipoprotein H is a single chain polypeptide composed of 326 amino acids highly glycosylated. Its carbohydrate content is approximately 19% of the molecular weight. We show that it is rich in sialic acid linked alpha (2-6) to galactose or N-acetylgalactosamine. Sialic acid is not alpha (2-3) linked to galactose. Galactose is beta (1-4) linked to N-acetylglucosamine and beta (1-3) linked to N-acetylgalactosamine. Carbohydrate O-linked chains (mainly sialic acid) are alpha (2-6) linked to galactose or N-acetylgalactosamine. Galactose is also organised in O-linked chains and beta (1-4) linked to N-acetylglucosamine and beta (1-3) linked to acetylgalactosamine. Concanavalin A lectin was used to isolate two groups of apolipoprotein H molecules bearing biantennary and truncated hybrids and high mannose and hybrid oligosaccharides. Apolipoprotein H fails to bind lysine-Sepharose. Our results thus show that it presents truncated hybrid or hybrid-type carbohydrate chains which bear few unmasked mannose residues as a terminal sugar. Biochemical analysis of carbohydrate structures conducted on single isoforms separated through IEF revealed that no specific carbohydrate complex is bound to a single isoform.
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PMID:Study of the glycosylation of apolipoprotein H. 1070 Oct 81

Apolipoprotein H (apoH, protein; APOH, gene) is a 50-kDa glycoprotein that binds to negatively charged substrates, including phospholipids. ApoH is a main target antigen for the binding of antiphospholipid antibodies that are associated with thrombotic events. We have previously characterized the structural organization of the human APOH gene. Because of the significant structural homology between the human and chimpanzee genomes, we have employed oligonucleotides from the human APOH gene sequence to amplify chimpanzee DNA covering the entire transcribed region together with flanking sequence in the 5' region. As in humans, the chimpanzee APOH gene consists of eight exons and seven introns and encodes for a 326-amino-acid protein. The deduced amino acid and nucleotide sequence show 99.4% and 99.6% similarity between human and chimpanzee APOH, respectively. Using isoelectric focusing (IEF) and immunoblotting, we screened 155 chimpanzees (128 unrelated captured parents and 27 captive-born offspring) for the apoH protein polymorphism. The most common IEF pattern in chimpanzees was identical to a previously described APOH*3 allele in humans. In addition, an anodally shifted pattern was observed in chimpanzees with an allele frequency of 0.168, and the corresponding allele was designated as APOH*4. DNA sequencing of APOH*4 carriers revealed a missense mutation in exon 6 (A-->G) at codon 210, which replaces the amino acid lysine by glutamic acid. This mutation does not affect the binding of apoH to cardiolipin as revealed by cardiolipin/enzyme-linked immunosorbent assay (ELISA). We also evaluated the prevalence of anti-apoH antibodies in chimpanzee plasma by using human-apoH-based ELISA and the association of the Lys210Glu mutation with the occurrence of anti-apoH antibodies. The prevalence of anti-apoH antibodies in chimpanzees (64%) was found to be unusually high compared with that found in humans. However, the Lys210Glu mutation showed no association with the occurrence of anti-apoH antibodies. The prevalence of anti-apoH antibodies in chimpanzees may serve as a useful animal model for the human antiphospholipid syndrome, where these antibodies are associated with clinical manifestations.
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PMID:Chimpanzee apolipoprotein H (beta2-glycoprotein I): report on the gene structure, a common polymorphism, and a high prevalence of antiphospholipid antibodies. 1147 37

Complexes formed between beta2GPI (beta2-glycoprotein I), a human plasma protein, and biological membranes are considered to be targets of macrophages and antiphospholipid autoantibodies involved in autoimmune diseases, such as antiphospholipid syndrome or systemic lupus erythematosus. The positively charged lysine-rich fifth domain of beta2GPI facilitates its interaction with phospholipid membranes containing acidic phospholipids, which normally become exposed by apoptotic processes. In the present study, atomic force microscopy was applied to visualize the binding of beta2GPI to a mixed phospholipid model membrane at physiological ionic strength. On supported lipid bilayers the formation of supramolecular assemblies of the protein with a height of approx. 3.3 nm was observed, suggesting a lateral agglomeration of beta2GPI. Detailed analysis of kinetic constants using surface plasmon resonance revealed that the binding can be described by a two-state reaction model, i.e. a very fast interaction step, depending on the content of acidic phospholipids in the bilayer, and a second step with significantly lower k(on) and k(off) values. Taken together, our results suggest a biphasic interaction mechanism: a fast step of beta2GPI binding to negatively charged lipids, mainly based on electrostatic interactions, and a slower phase of agglomeration of the protein on the bilayer surface accompanied by a protein-induced rigidification of the membrane, as revealed by electron paramagnetic resonance.
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PMID:Membrane binding of beta2-glycoprotein I can be described by a two-state reaction model: an atomic force microscopy and surface plasmon resonance study. 1581 6

In the antiphospholipid syndrome (APS), pathogenic antiphospholipid antibodies (aPL) that cause thrombosis or pregnancy morbidity are characterized by binding to anionic phospholipids (PL) and beta2-glycoprotein I (beta(2)GPI). Sequence analysis of human monoclonal aPL has shown that high affinity for these antigens is associated with the presence of three particular amino acids: arginine (Arg), asparagine and lysine in the complementarity determining regions (CDRs) of their heavy and light chains. In vitro expression systems have been used to create variants of the antibodies in which these amino acids have been altered. In general, removal of Arg residues reduces affinity for anionic PL and beta(2)GPI. Arg at different positions in the sequence, however, have different effects on binding affinity and effects on binding are not always mirrored by effects on pathogenicity. This review will focus upon the sequence motifs that have been found to distinguish pathogenic from non-pathogenic aPL, and whether these or other properties may help to identify distinct pathogenic subsets of aPL. In particular, we will focus on our recent work in which we are trying to develop a better understanding of the molecular mechanisms involved in activation of target cells by pathogenic aPL. These studies, together with molecular models of antigen/antibody complexes, help us to understand exactly how pathogenic antibodies interact with antigens. Ultimately, this understanding may aid the design of more powerful diagnostic/prognostic assays and targeted therapeutic agents to block the pathogenic effects of these antibodies.
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PMID:Examining the non-linear relationship between monoclonal antiphospholipid antibody sequence, structure and function. 1882 54

One of the major problems in the study of the dynamics of proteins is the visualization of changing conformations that are important for processes ranging from enzyme catalysis to signaling. A protein exhibiting conformational dynamics is the soluble blood protein beta 2-glycoprotein I (beta2GPI), which exists in two conformations: the closed (circular) form and the open (linear) form. It is hypothesized that an increased proportion of the open conformation leads to the autoimmune disease antiphospholipid syndrome (APS). A characteristic feature of beta2GPI is the high content of lysine residues. However, the potential role of lysine in the conformational dynamics of beta2GPI has been poorly investigated. Here, we report on a strategy to permanently open up the closed protein conformation by chemical acetylation of lysine residues using acetic acid N-hydroxysuccinimide ester (NHS-Ac). Specific and complete acetylation was demonstrated by the quantification of primary amino groups with fluoraldehyde o-phthalaldehyde (OPA) reagent, as well as western blot analysis with an anti-acetylated lysine antibody. Our results demonstrate that acetylated beta2GPI preserves its secondary and tertiary structures, as shown by circular dichroism spectroscopy. We found that after lysine acetylation, the majority of proteins are in the open conformation as revealed by atomic force microscopy high-resolution images. Using this strategy, we proved that the electrostatic interaction of lysine residues plays a major role in stabilizing the beta2GPI closed conformation, as confirmed by lysine charge distribution calculations. We foresee that our approach will be applied to other lysine-rich proteins (e.g. histones) undergoing conformational transitions. For instance, conformational dynamics can be triggered by environmental conditions (e.g. pH, ion concentration, post-translational modifications, and binding of ligands). Therefore, our study may be relevant for investigating the equilibrium of protein conformations causing diseases.
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PMID:Lysine residues control the conformational dynamics of beta 2-glycoprotein I. 3017 30


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