Antigenic structure of human hemoglobin: Delineation of the antigenic site (site 2) within region 41?65 of the alpha chain by immunochemistry of synthetic peptides

Lysine conjugate of acrylonitrile as antigenic sites in hemoglobin adducts

For biomonitoring environmental exposure to acrylonitrile (AN), a monoclonal antibody (mAb) A2D1, was developed to recognize specifically the hemoglobin (Hb) adduct, Hb-AN, but not Hb itself. This appears to be the first example that a small molecule-like AN may introduce new antigenicity into hemoglobin, which already exhibits multiple antigenic determinants. This report addresses the localization of the newly formed antigenic sites in human Hb-AN. As antigenic probes, the AN conjugates of 10 amino acids, six dipeptides, and four tripeptides were prepared as monitored by 1H NMR, and their antigenicity was evaluated by competitive inhibition immunoassay. A Lys-epsilonNH-AN was found essential to inhibiting activity. The potent peptide-AN inhibitors, containing a sequence of His and Lys, showed IC50 at the micromolar concentration, thus implicating human Hbalpha-89,90 and Hbbeta-143,144 in the distal heme pocket region as the new antigenic sites.

Analysis of human follistatin structure: identification of two discontinuous N-terminal sequences coding for activin A binding and structural consequences of activin binding to native proteins

A primary physiological function of follistatin is the binding and neutralization of activin, a transforming growth factor-beta family growth factor, and loss of function mutations are lethal. Despite the critical biological importance of follistatin's neutralization of activin, the structural basis of activin's binding to follistatin is poorly understood. The purposes of these studies were 1) to identify the primary sequence(s) within the N-terminal domain of the follistatin coding for activin binding, and 2) to determine whether activin binding to the native protein causes changes in other structural domains of follistatin. Synthetic peptide mimotopes identified within a 63-residue N-terminal domain two discontinuous sequences capable of binding labeled activin A. The first is located in a region (amino acids 3-26) of follistatin, a site previously identified by directed mutagenesis as important for activin binding. The second epitope, predicted to be located between amino acids 46 and 59, is newly identified. Although the sequences 3-26 and 46-59 code for activin binding, native follistatin only binds activin if disulfide bonding is intact. Furthermore, pyridylethylation of Cys residues followed by N-terminal sequencing and amino acid analysis revealed that all of the Cys residues in follistatin are involved in disulfide bonds and lack reactive free sulfhydryl groups. Specific ligands were used to probe the structural effects of activin binding on the other domains of the full-length molecule, comprised largely of the three 10-Cys follistatin module domains. No effects on ligand binding to follistatin-like module I or II were observed after the binding of activin A to native protein. In contrast, activin binding diminished recognition of domain III and enhanced that of the C domain by their respective monoclonal antibody probes, indicating an alteration of the antigenic structures of these regions. Thus, subsequent to activin binding, interactions are likely to occur between regions of follistatin located in different domains and separated by considerable lengths of linear sequence. Such interactions could have important functional significance with respect to the structural heterogeneity of naturally occurring follistatins.

Production of antibodies against murine class II antigens using unconjugated synthetic peptides of the beta chain region 63-78

synthetic peptides corresponding to residues 63-78 of the first domain of the beta chain of murine I-A/I-E class II antigens were used in the unconjugated rather than the traditional protein-conjugated form to immunize (129J X B6)F1 mice. The sequences made represented the four haplotypes; Ak beta, Ad beta, Abm-12 beta and Ed beta. These sequences were selected on the basis of computer algorithms used to predict surface accessibility and main-chain flexibility profiles, and by reported hypervariability and site-directed mutagenesis experiments of these regions. Factors such as the use of complete Freund's adjuvant, a continuous immunization regime, and the sex of the mice used were found to influence the amount of anti-peptide antibody produced when unconjugated peptide was used as the immunogen. Antibodies produced were shown by FACS analysis to react with I-A/I-E class II antigens expressed on the lymphocyte surface. These findings indicate that the use of unconjugated synthetic peptides representing sequences of proteins which are in close proximity to disulfide bonds may be an advantage over conventional methods of peptide conjugation to proteins.

Recognition of inter-transmembrane regions of acetylcholine receptor alpha subunit by antibodies, T cells and neurotoxins. Implications for membrane-subunit organization

Three regions of the alpha chain of Torpedo californica acetylcholine receptor (AChR), corresponding to residues alpha 262-276, alpha 388, 408 and alpha 427-437 were synthesized, purified and characterized. The first two peptides have been proposed to occupy inter-transmembrane regions while the third represented the C-terminal segment, proposed by various models to be either extracellular or intracellular. Peptide alpha 388-408 stimulated a good response in the AChR-primed T cells of H-2s haplotype mice, a low response in the H-2q haplotype and no response in the H-2b haplotype. Peptide alpha 427-437 stimulated AChR-primed T cells of the H-2s haplotype, but caused no response in the q and b haplotypes. Peptide alpha 262-276 evoked no in vitro stimulation in any of the s, q or b haplotypes. In antibody binding studies, peptide alpha 388-408 bound antibodies raised against free AChR or against membrane-bound AChR. The other two peptides showed little or no binding activity. Further, peptide alpha 388-408 bound specifically both 125I-labelled bungarotoxin and cobratoxin, while the other two peptides had no binding activity. These results were consistent with only one of the models for subunit organization within the membrane.

Studies with antibodies against the conserved cysteine region of progesterone receptor

Polyclonal antibodies were generated against two synthetic peptides corresponding to sequences from the DNA-binding domain of steroid receptors. The sequence for peptide 1 (13 amino acids) lies between the two putative metal-binding loops of the conserved cysteine region while the sequence for peptide 2 (12 amino acids) lies within one loop. Peptide antibodies were generated by injecting rabbits with peptide conjugated to bovine serum albumin. By Western blot analysis, antibodies to peptide 2 recognized chick and human progesterone receptor and human glucocorticoid receptor, but peptide 1 antibodies did not. No cross-reactivity with native chick progesterone receptor was detected with either anti-peptide. These findings suggest that the epitopes for peptide 2 antibodies, and possibly for peptide 1 antibodies, are inaccessible to antibody in the native receptor.

Rapid degradation of neurotensin by intact murine neuroblastoma cells (clone N1E-115)

Murine neuroblastoma clone N1E-115, which possesses receptors for neurotensin mediating the formation of intracellular cyclic GMP and the stimulation of inositol phospholipid hydrolysis, exhibited only partial desensitization to neurotensin. This result led to the observation that neurotensin was very rapidly degraded by intact N1E-115 cells. In experiments measuring the time course of [3H]neurotensin degradation, a minimum of six major tritiated products were found, with the breakdown peptides formed and the degree of proteolysis of [3H]neurotensin being dependent upon the length of incubation and the concentration of cells. Clone N1E-115 degraded [3H]neurotensin in an apparently sequential fashion; the primary initial cleavage of intact neurotensin was at the peptide bond between residues Arg8 and Arg9. Initial degradation peptides from the active carboxyl-terminal portion of neurotensin were more rapidly degraded, after formation, than were the peptides from the inactive amino-terminal half of neurotensin. The final two degradation products found were tyrosine, from the carboxyl-terminal portion of neurotensin, and an as yet unidentified peptide from the amino-terminal half of neurotensin. [3H]Neurotensin(8-13) was more rapidly hydrolyzed under identical conditions than was [3H]neurotensin itself. A combination of the protease inhibitors 1,10-phenanthroline and Z-Pro-Prolinal was able to inhibit almost completely the degradation of neurotensin by clone N1E-115.

Segment alpha 182-198 of Torpedo californica acetylcholine receptor contains second toxin-binding region and binds anti-receptor antibodies

The area around Cys-192 and Cys-193 is thought to be a functionally important part of the alpha-subunit of the acetylcholine receptor. We have synthesized peptide alpha 182-198 of the alpha-chain of the Torpedo californica acetylcholine receptor and investigated the binding to the peptide of alpha-bungarotoxin, cobratoxin and antibodies raised against acetylcholine receptor. The results showed that the synthetic peptide alpha 182-198 contains a second toxin-binding region and also binds a considerable fraction of anti-receptor antibodies. We also report here the toxin-binding activity of synthetic peptide alpha 125-148 of the human acetylcholine receptor which has been previously localized as a toxin-binding region in the alpha-chain of the Torpedo receptor.