Analysis of exposed regions on the main extracellular domain of mouse acetylcholine receptor α subunit in live muscle cells by binding profiles of antipeptide antibodies

To study the structural organization of the main extracellular domain of the nicotinic acetylcholine receptor (AChR) subunit in live muscle cells, we examined the native membrane-bound receptors in cultured mouse skeletal muscle cells for their ability to bind a panel of antibodies against uniform-sized overlapping synthetic peptides which collectively represent this entire domain. The binding profile indicated that the regions 23–49,78–126,146–174, and182–210 are accessible to binding with antibody. Residues23–49,78–126, and194–210 contain binding regions for-neurotoxin and some myasthenia gravis autoantibodies. A comparison of this binding profile with the profile obtained for membrane-boundTorpedo californica AChR in isolated membrane fractions showed some similarities as well as significant differences between the subunit organization in the isolated membrane fraction and that in the membrane of live muscle cells. Regions89–104 and158–174, which are exposed in the isolated membrane fraction, are also exposed in the live cell. On the other hand, regions23–49, and182–210, which are exposed in the live cell, are not accessible in the isolated membrane and, furthermore, the region1–16, which has marginal accessibility in the cell, becomes highly accessible in the membrane isolates. The exposed regions defined by this study may be the primary targets for the initial autoimmune attack on the receptors in experimental autoimmune myasthenia gravis.     

Genetic control of immune response to sperm whale myoglobin in mice. I. T lymphocyte proliferative response under H-2-linked Ir gene control.

Studies on the genetic control of immune response to sperm whale myoglobin were initiated. As demonstrated in this paper, the T lymphocyte proliferative response to whale myoglobin is under H-2-linked Ir gene control. Mice of H-2d, H-2f, and H-2s haplotypes were high responders to the myoglobin, whereas haplotypes H-2b, H-2k, H-2p, H-2q, and H-2r were low responders. The Ir gene(s) was localized between H-2K and H2D regions, since the recombinant strain A.TL (KsIkSkDd) was a low responder and A.TH (KsIsSsDd) was a high responder. Further studies with recombinant strains revealed that the expression of the high-responder I-Ad or Ias alleles was sufficient to give a good response, since strains D2.GD (d d b b b b b b) and B10.HTT (s s s s k k k d) were high responders. The expression of the I-Cd allele in strains B10.A (k k k k k d d d) and B10.A(5R) (b b b k k d d d) also gave high response, and thus suggested a second Ir gene, derived from the H-2d haplotype. The finding that expression of the I-Cs allele in B10.S(8R) (k k ? ? s s s s) did not result in high response suggests the lack of the second Ir gene in the high-responder H-2s haplotype.     

Localization of the continuous allergenic sites of ragweed allergen Ra3 by a comprehensive synthetic strategy

A comprehensive synthetic approach, previously introduced by this laboratory for the localization of the full profile of the continuous antigenic sites on proteins, was applied here to localize the continuous sites of ragweed allergen, Ra3, that are recognized by human anti-Ra3 IgE antibodies. The following 10 uniform and overlapping peptides were synthesized and purified: 1-15, 11-25, 21-35, 31-45, 41-55, 51-65, 61-75, 71-85, 81-95 and 91-101. Quantitative radiometric titrations of protein and peptide adsorbents with human IgE, established the full profile of allergenic (IgE binding) sites on Ra3. It was found that Ra3 has four continuous allergenic sites. Antibodies prepared against the IgE binding peptides bound to native Ra3. The findings are briefly discussed in relation to other protein antigenic structures and in terms of design of vaccines using synthetic sites.     

Progranulin directly binds to the CRD2 and CRD3 of TNFR extracellular domains

We previously reported that PGRN directly bound to TNF receptors (TNFR) in vitro and in chondrocytes (Tang, et al., Science, 2011). Here we report that PGRN also associated with TNFR in splenocytes, and inhibited the binding of TNFα to immune cells. Proper folding of PGRN is essential for its binding to TNFR, as DTT treatment abolished its binding to TNFR. In contrast, the binding of PGRN to Sortilin was enhanced by DTT. Protein interaction assays with mutants of the TNFR extracellular domain demonstrated that CRD2 and CRD3 of TNFR are important for the interaction with PGRN, similar to the binding to TNFα. Taken together, these findings provide the molecular basis underlying PGRN/TNFR interaction and PGRN-mediated anti-inflammatory activity in various autoimmune diseases and conditions.     

A peptide-based immunoassay for antibodies against botulinum neurotoxin A

Cervical dystonia (CD) is due to neck-muscle spasms that cause pain and involuntary contractions resulting in abnormal neck movements and posture. Symptoms can be relieved by injecting the affected muscle with a botulinum neurotoxin (BoNT, usually type A or type B). The therapeutic benefits are impermanent and toxin injections need to be repeated every 3-6 months. In a very small percentage of patients (less with BoNT/A than with BoNT/B) the treatment elicits blocking anti-toxin antibodies (Abs), which reduce or terminate the patient's responsiveness to further treatment. We have recently mapped (Dolimbek et al., 2006) the CD sera Ab-binding profile using a panel of 60, 19-residue peptides that encompassed the entire H chain sequence 449-1296 and overlapped consecutively by 5 residues. Abs in CD sera bound to one or more of the peptides N25, C10, C15, C20, and C31. This suggested the possibility that binding to these peptides could be used for assay of Abs in CD sera. Data analysis reported here found that Ab binding to these regions showed very significant deviations from the control responses. Of these four peptides, C10 showed the most significant level of separation between patient and control groups (p = 5 x 10(-7)) and the theoretical resolution (i.e., ability to distinguish CD patients from control, see full definition under 'Statistical analysis' in Methods), 84%, was about 4% higher than the least resolved response, C31 (p = 6 x 10(-6), resolution 80%). Since the amounts of Abs bound to a given peptide varied with the patient and not all the patients necessarily recognized all four peptides, there was the possibility that binding to combinations of two or more peptides might give a better discriminatory capability. Using two peptides, C10 plus C31, the resolution improved to 87% (p = 4 x 10(-8)). These two peptides appeared to compliment each other and negate the lower resolution of C31. Combination of three peptides gave resolutions that ranged from 85 (N25 + C15 + C31; p = 2 x 10(-7)) to 88% (C10 + C15 + C31; p = 1 x 10(-8)). Finally, using the data of all four peptides, N25 + C10 + C15 + C31, gave a resolution of 86% (p = 1 x 10(-7)). Although these levels of resolution are somewhat lower than that obtained with whole BoNT/A (resolution 97%; p = 6 x 10(-12)), it may be concluded that the two-peptide combination C10 + C31, or the three-peptide combination C10 + C15 + C31 (affording resolutions of 87 and 88%, respectively) provide a good diagnostic, toxin-free procedure for assay of total specific anti-toxin Abs in BoNT/A-treated CD patients.