Selection of antibody probes to correlate protein sequence domains with their structural distribution.
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We propose a new approach that permits correlation of specific domains defined by their primary sequence with their location in the structure of complex macromolecular aggregates. It is based on the combination of well-established structural analysis methods that incorporate the use of overlapping peptides on cellulose membranes for the isolation and purification of specific antibodies from a polyclonal antiserum. Monospecific antibodies to the connector protein of bacteriophage phi29 were isolated from polyclonal antisera using a new development of the spotscan method. These antibodies can be purified in quantities that allow antigenicity testing in enzyme-linked immunosorbent assays, Western blotting and immunoprecipitations, demonstrating the specificity of this isolation procedure. This approach has allowed us to generate direct antibody probes for immunoelectron microscopy mapping of different connector protein domains in a low resolution three-dimensional epitope map. (+info)
Quantifying the exact role of HLA-DRB1 alleles in susceptibility to inflammatory polyarthritis: results from a large, population-based study.
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OBJECTIVE: To accurately determine the contributions of HLA-DRB1 alleles in explaining susceptibility to inflammatory polyarthritis in a large, true population-based cohort of new-onset cases. METHODS: A cohort of 680 consecutive patients with inflammatory polyarthritis, of whom 404 satisfied the American College of Rheumatology (ACR) criteria for rheumatoid arthritis (RA), was recruited from the population-based Norfolk Arthritis Register. All cases were compared with 286 local population controls. A standardized clinical assessment was performed on all patients. HLA-DRB1 phenotypes, including DR4 subtypes, were determined using a semiautomated, reverse dot-blot method. Results were expressed as odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: There was only a modest association (OR 1.8, 95% CI 1.4-2.4) between inflammatory polyarthritis and the presence of any shared epitope (SE) allele; the strongest individual risk was with DRB1*0404 (OR 3.5, 95% CI 1.8-6.8). Comparison of the genotypes demonstrated that the effect of being SE homozygous (OR 2.1, 95% CI 1.5-3.0) was only moderately greater than the effect of being SE heterozygous (OR 1.3, 95% CI 1.1-1.6). The exception to this was genotypic combinations that included HLA-DRB1*0404, which exhibited ORs ranging up to 18.0. There were no differences between either the phenotype or genotype data when the patients were stratified by RA status (defined by the ACR criteria). In contrast, the associations were substantially stronger in patients who were positive for rheumatoid factor. CONCLUSION: Previous studies had not been able to clarify whether the influence of HLA-DRB1 on RA was related to disease susceptibility or to disease severity and progression. These data on a unique population-based incident cohort suggest only weak effects on susceptibility, with the exception of the clearly distinct influence of HLA-DRB1*0404. (+info)
Bidirectional transmembrane modulation of integrin alphaIIbbeta3 conformations.
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Activation of blood platelets by physiological stimuli (e.g. thrombin, ADP) at sites of vascular injury induces inside-out signaling, resulting in a conformational change of the prototype integrin alphaIIbbeta3 from an inactive to an active state competent to bind soluble fibrinogen. Furthermore, ligand occupancy of alphaIIbbeta3 initiates outside-in signaling and additional conformational changes of the receptor, leading to the exposure of extracellular neoepitopes termed ligand-induced binding sites (LIBS), which are recognized by anti-LIBS monoclonal antibodies. To date, the mechanism of bidirectional transmembrane signaling of alphaIIbbeta3 has not been established. In this study, using our newly developed anti-LIBScyt1 monoclonal antibody, we showed that extracellular ligand binding to alphaIIbbeta3 on blood platelets induces a transmembrane conformational change in alphaIIbbeta3, thereby exposing the LIBScyt1 epitope in the alphaIIb cytoplasmic sequence between Lys994 and Asp1003. In addition, a point mutation at this site (P998A/P999A) renders alphaIIbbeta3 constitutively active to bind extracellular ligands, resulting in fibrinogen-dependent cell-cell aggregation. Taken collectively, these results demonstrated that the extracellular ligand-binding site and a cytoplasmic LIBS epitope in integrin alphaIIbbeta3 are conformationally and functionally coupled. Such bidirectional modulation of alphaIIbbeta3 conformation across the cell membrane may play a key role in inside-out and outside-in signaling via this integrin. (+info)
The antigenicity of tobacco mosaic virus.
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The antigenic properties of the tobacco mosaic virus (TMV) have been studied extensively for more than 50 years. Distinct antigenic determinants called neotopes and cryptotopes have been identified at the surface of intact virions and dissociated coat protein subunits, respectively, indicating that the quaternary structure of the virus influences the antigenic properties. A correlation has been found to exist between the location of seven to ten residue-long continuous epitopes in the TMV coat protein and the degree of segmental mobility along the polypeptide chain. Immunoelectron microscopy, using antibodies specific for the bottom surface of the protein subunit, showed that these antibodies reacted with both ends of the stacked-disk aggregates of viral protein. This finding indicates that the stacked disks are bipolar and cannot be converted directly into helical viral rods as has been previously assumed. TMV epitopes have been mapped at the surface of coat protein subunits using biosensor technology. The ability of certain monoclonal antibodies to block the cotranslational disassembly of virions during the infection process was found to be linked to the precise location of their complementary epitopes and not to their binding affinity. Such blocking antibodies, which act by sterically preventing the interaction between virions and ribosomes may, when expressed in plants, be useful for controlling virus infection. (+info)
Identification of novel sites in the ovine growth hormone receptor involved in binding hormone and conferring species specificity.
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Using site-directed mutagenesis we mutated the extracellular domain of the ovine growth hormone receptor (oGHR) to the corresponding amino acids in the rat GHR at two different sites: site A is between Thr28 and Leu34 and represents a major immunogenic epitope, while site B is between Ser121 and Asp124 and is involved in the interaction of the human GHR with growth hormone (GH). Native and mutant receptors were bacterially expressed and refolded, and then RIA and GH-binding assays were carried out on the purified recombinant proteins. Mutations at the N-terminal site A of oGHR led to greatly reduced binding to bovine GH and, in addition, to significant loss of recognition by a polyclonal antiserum to bovine GHR which recognizes site A as a major epitope. The crystal structure of human GH bound to human GHR did not resolve this extreme N-terminal region of the receptor but our data indicate that the N-terminal loop undertakes a 180 degrees turn bringing it into close proximity to the hormone-binding domain in a fashion analogous to the prolactin receptor. A fourfold decrease in affinity for binding bovine GH was also observed after mutation of site B. However, this change from the ovine sequence to the equivalent sequence in the rat GHR at site B caused a 2.4-fold increase in the affinity of binding to rat GH. Taken together, the changes in binding affinity of the site-B mutant for rat and bovine GH demonstrate that this site is involved in conferring species specificity for binding GH. (+info)
Construction of a human platelet alloantigen-1a epitope(s) within murine glycoprotein IIIa: identification of residues critical to the conformation of the antibody binding site(s).
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The human platelet alloantigen 1 system (HPA-1) is determined by a polymorphism at position 33 in the N-terminus of human glycoprotein IIIa (GPIIIa). This naturally occurring substitution creates a conformation in the HPA-1a allelic form that can be antigenic when presented to an individual expressing the HPA-1b form. Anti-HPA-1a antibodies generated by this immune response can lead to the destruction of platelets, as seen in the clinical disorders, neonatal alloimmune thrombocytopenia (NAIT) and posttransfusion purpura (PTP). To understand better the structural requirements for recognition by these pathogenic antibodies, we investigated the N-terminal 66 amino acids from the HPA-1a form of human GPIIIa and the analogous amino acids from the nonimmunogenic murine homolog. Our objectives were to define further the boundaries of the HPA-1a epitope(s) in the N-terminus of human GPIIIa, to isolate the murine 5' nucleotide sequence and compare the deduced murine N-terminal sequence to that of human, and to mutate the murine sequence systematically to include an HPA-1a epitope(s). Murine amino acids that differed from human were changed by site-directed mutagenesis to the analogous residues in the HPA-1a form of human GPIIIa, starting and radiating from murine position 33 (site of human polymorphism). This systematic approach allowed us to pinpoint amino acids critical to a conformation recognized by anti-HPA-1a antibodies. Our results show that an HPA-1a epitope can be created within the N-terminus of murine GPIIIa and raise the possibility that murine models of HPA-1a sensitization can be developed. (+info)
Monoclonal antibody 3H8: a useful tool in the diagnosis of candidiasis.
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In a previous series of experiments six mAbs were obtained against cell wall extracts of Candida albicans ATCC 26555. After several studies only one of them, designated 3H8, has been used to produce a commercial kit for the rapid diagnosis of candidiasis, Bichro-latex albicans (Fomouze Diagnostics). The present study involved the generation and characterization of this mAb as an immunoglobulin G1 which recognizes mannoproteins of high molecular mass present in the C. albicans cell wall. ELISA assays showed that the presence of the epitope recognized by mAb 3H8 was similar in both yeast and mycelial cell walls of C. albicans, in contrast to the epitope for mAb 1B12, which is mainly expressed in the yeast cell wall. The 3H8 epitope was located at the external surface in C. albicans ATCC 26555, whereas it is partially cryptic in the cell wall in other C. albicans strains. No reaction was observed with other Candida species. Immunohistochemical studies using this antibody demonstrated that it specifically recognized C. albicans in tissue, detecting mycelial forms and, to a lesser extent, blastospores, suggesting that it is also a valuable tool in the evaluation of fungal infections in paraffin-embedded tissue, particularly when identification is required. (+info)
Prevention of experimental antiphospholipid syndrome and endothelial cell activation by synthetic peptides.
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Antiphospholipid syndrome (APS) is characterized by recurrent fetal loss, repeated thromboembolic phenomena, and thrombocytopenia. The syndrome is believed to be caused by antiphospholipid beta-2-glycoprotein-I (beta2GPI)-dependent Abs or anti-beta2GPI Abs by themselves. Using a hexapeptide phage display library, we identified three hexapeptides that react specifically with the anti-beta2GPI mAbs ILA-1, ILA-3, and H-3, which cause endothelial cell activation and induce experimental APS. To enhance the binding of the peptides to the corresponding mAbs, the peptides were lengthened to correspond with the site of the beta2GPI epitope being recognized by these mAbs. As a result, the following three peptides were prepared: A, NTLKTPRVGGC, which binds to ILA-1 mAb; B, KDKATFGCHDGC, which binds to ILA-3 mAb; and C, CATLRVYKGG, which binds to H-3 mAb. Peptides A, B, and C specifically inhibit both in vitro and in vivo the biological functions of the corresponding anti-beta2GPI mAbs. Exposure of endothelial cells to anti-beta2GPI mAbs and their corresponding peptides led to the inhibition of endothelial cell activation, as shown by decreased expression of adhesion molecules (E-selectin, ICAM-1, VCAM-1) and monocyte adhesion. In vivo infusion of each of the anti-beta2GPI mAbs into BALB/c mice, followed by administration of the corresponding specific peptides, prevented the peptide-treated mice from developing experimental APS. The use of synthetic peptides that focus on neutralization of pathogenic anti-beta2GPI Abs represents a possible new therapeutic approach to APS. (+info)