Biomedical subjects

P T Wilson

Publications and source records attributed to P T Wilson.

At least 19 recordsLinked to original sources

PubMed1990

Monoclonal antibodies directed against a synthetic peptide corresponding to the alpha-bungarotoxin binding region of the acetylcholine receptor.

Murine monoclonal antibodies have been produced against a 32 amino acid synthetic peptide corresponding to residues 173-204 on the alpha-subunit of the nicotinic acetylcholine receptor from Torpedo californica. All of the monoclonal antibodies were of the IgM subtype and most cross-reacted with the purified native receptor. None of the antibodies were effective in blocking alpha-bungarotoxin binding to the receptor nor, conversely, did alpha-bungarotoxin interfere with antibody binding. However, two monoclonal antibodies, previously shown to bind near the ligand binding site on the native receptor, did compete partially (50%) with the binding of one of the IgM monoclonal antibodies.

Animals↗

PubMed1988

Binding of alpha-bungarotoxin to synthetic peptides corresponding to residues 173-204 of the alpha subunit of Torpedo, calf, and human acetylcholine receptor and restoration of high-affinity binding by sodium dodecyl sulfate.

In order to investigate structure-function relationships of a segment of the acetylcholine receptor alpha subunit, binding of alpha-bungarotoxin to synthetic peptides corresponding to residues 173-204 of Torpedo, calf, and human alpha subunits was compared using a solid-phase radioassay. The affinities of 125I-alpha-bungarotoxin for the calf and human peptides were 15- and 150-fold less, respectively, than for the Torpedo peptide. On the basis of nonconservative substitutions in the calf and human sequences, aromatic residues (Tyr-181, Trp-187, and Tyr-189) are important for the higher affinity binding of the Torpedo peptide. Substitution of negatively charged Glu-180 with uncharged Gln in the calf peptide did not significantly affect toxin binding, indicating Glu-180 alone does not comprise the anionic subsite on the receptor to which the cationic quaternary ammonium groups of cholinergic agents bind. d-Tubocurarine competed toxin binding to the modified calf 32-mer which lacks Glu-180 and Asp-195 present in Torpedo. Thus, the negative subsite could be formed by another negatively charged residue or by more than one amino acid side chain. It is possible that the positive charges on cholinergic ligands are countered by a negative electrostatic potential provided by polar groups, such as the hydroxyl group of tyrosine, present on several residues in this region, and the negative charges present on any of residues 175, 180, 195, or 200. Equilibrium saturation binding of alpha-bungarotoxin to Torpedo peptide 173-204 revealed a minor binding component with an apparent KD of 4.2 nM and a major component with a KD of 63 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Neurotoxin-binding site on the acetylcholine receptor.

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Animals↗

PubMed1988

Synthetic peptides in the study of the interaction of rabies virus and the acetylcholine receptor.

The neurotropism of some viruses may be explained in part by the attachment of these viruses to host cell receptors that are present on or even largely restricted to neurons. Rabies virus is an RNA virus that, after a period of replication in muscle, gains access to the central nervous system, where it selectively infects certain neuronal populations. The nicotinic acetylcholine receptor occurs in high density at the neuromuscular junction and is present in the central nervous system. Although several different cell surface constituents may act as attachment determinants for rabies, direct binding of radioactively labeled virus to affinity-purified acetylcholine receptor has been demonstrated. Binding of virus to the receptor was saturable and inhibited by up to 50% by alpha-bungarotoxin, a snake venom neurotoxin that binds at or near the acetylcholine binding site on the receptor. The molecular basis for the virus-receptor interaction may lie in an amino acid sequence similarity between the snake venom neurotoxins and a segment of the rabies virus glycoprotein. Two peptides (10 and 13 residues) of the rabies virus glycoprotein and homologous bungarotoxin peptides were synthesized and tested for ability to compete with labeled alpha-bungarotoxin for binding to the acetylcholine receptor. The peptides were found to compete with toxin binding with affinities comparable to those of the cholinergic ligands d-tubocurarine and nicotine. These findings indicate that a segment of the rabies virus glycoprotein interacts with the acetylcholine receptor at or near the acetylcholine binding site of the receptor. The similarity between the virus glycoprotein and the neurotoxin was further evidenced by the cross reaction of antibody raised against the virus 10-mer with the bungarotoxin 10-mer. Binding of rabies virus to the acetylcholine receptor or to other neuronal bungarotoxin-binding proteins may be related to the neurotropism of this virus. In addition, knowledge of both the region of the virus involved in binding and the binding domain on the receptor may be helpful in developing new strategies for treatment, especially for viruses that infect the central nervous system or evade the immune response through genetic drift. These strategies include development of antiviral agents that cross the blood-brain barrier and inhibit viral binding and the utilization as immunogens the regions of viruses, such as their binding domains, that are highly conserved among different strains.

Animals↗

PubMed1988

Distribution of alpha-bungarotoxin binding sites over residues 173-204 of the alpha subunit of the acetylcholine receptor.

The binding of alpha-bungarotoxin to several synthetic peptides comprising different segments of the region 173-204 of the alpha subunit of the Torpedo acetylcholine receptor was investigated to further localize the neurotoxin-binding site on the primary sequence. When tested in a solid phase microwell assay system, a 32-amino acid peptide corresponding to residues 173-204 (32-mer) bound 125I-alpha-bungarotoxin with the same affinity (4.2 x 10(-8) M as determined from IC50 values) as the isolated alpha subunit (4.6 x 10(-8) M). The relative affinities of other antagonists (alpha-cobratoxin, d-tubocurarine) maintained the same rank order in this assay system as has been demonstrated with the intact receptor. Agonists competed with binding of toxin at millimolar concentrations but lost all rank order of potency. These findings demonstrate that peptide 173-204 contains many of the antagonist-binding determinants present on denatured alpha subunit but has lost specificity of agonist binding. To further localize the toxin-binding site, alpha-bungarotoxin binding to seven shorter peptides corresponding to portions of the 32-mer was investigated. 125I-alpha-Bungarotoxin bound to alpha subunit peptides 179-192, 181-198, 185-196, 186-196, and 193-204, but not to alpha subunit peptides 173-180 and 194-204. In a second assay, all of the peptides competed with binding of 125I-acetylcholine receptor to immobilized alpha-bungarotoxin. The apparent affinity was highest for the 173-204 32-mer (1.4 x 10(-7) M) and lowest for peptides 173-180 and 194-204 (greater than 10(-4) M). The affinity of the other peptides was intermediate (approximately 10(-5) M) and about 100-fold less than that of the 32-mer. The affinity of alpha-bungarotoxin was 3.5 x 10(-10) M, of isolated, native acetylcholine receptor, 3.2 x 10(-9) M, and of isolated denatured subunit, 1.2 x 10(-8) M, with this assay. The retention of some toxin-binding capacity by the shorter peptides indicates toxin-binding determinants are distributed over the entire length of the 32-mer. The determinants with higher affinity are located in the central region of the 32-mer between residues 179 and 196.

Animals↗

PubMed1987

Synthetic peptides corresponding to sequences of snake venom neurotoxins and rabies virus glycoprotein bind to the nicotinic acetylcholine receptor.

Peptides corresponding to portions of loop 2 of snake venom curare-mimetic neurotoxins and to a structurally similar region of rabies virus glycoprotein were synthesized. Interaction of these peptides with purified Torpedo electric organ acetylcholine receptor was tested by measuring their ability to block the binding of 125I-labeled alpha-bungarotoxin to the receptor. In addition, inhibition of alpha-bungarotoxin binding to a 32-residue synthetic peptide corresponding to positions 173-204 of the alpha-subunit was determined. Neurotoxin and glycoprotein peptides corresponding to toxin loop 2 inhibited labeled toxin binding to the receptor with IC50 values comparable to those of nicotine and the competitive antagonist d-tubocurarine and to the alpha-subunit peptides with apparent affinities between those of d-tubocurarine and alpha-cobratoxin. Substitution of neurotoxin residue Arg37, the proposed counterpart of the quaternary ammonium of acetylcholine, with a negatively charged Glu residue reduced the apparent affinity about 10-fold. Peptides containing the neurotoxin invariant residue Trp29 and 10- to 100-fold higher affinities than peptides lacking this residue. These results demonstrate that relatively short synthetic peptides retain some of the binding ability of the native protein from which they are derived, indicating that such peptides are useful in the study of protein-protein interactions. The ability of the peptides to compete alpha-bungarotoxin binding to the receptor with apparent affinities comparable to those of other cholinergic ligands indicates that loop 2 of the neurotoxins and the structurally similar segment of the rabies virus glycoprotein act as recognition sites for the acetylcholine receptor. Invariant toxin residues Arg37 and Trp29 and their viral homologs play important, although not essential, roles in binding, possibly by interaction with complementary anionic and hydrophobic subsites on the acetylcholine receptor. The alpha-subunit peptide most likely contains all of the determinants for binding of the toxin and glycoprotein peptides present on the alpha-subunit, because these peptides bind to the 32-residue alpha-subunit peptide with the same or greater affinity as to the intact subunit.

Amino Acid Sequence↗

PubMed1986

Alpha-bungarotoxin binding to a high molecular weight component from lower vertebrate brain identified on dodecyl sulfate protein-blots.

The binding of [125I]iodo-alpha-bungarotoxin [( 125]alpha-BuTX) to the dissociated alpha-subunit of Torpedo acetylcholine receptor (AChR) can be readily demonstrated in a modified 'protein-blot' analysis utilizing electrophoretically transferred, dissociated subunits immobilized onto positively charged nylon membranes which are then incubated directly with [125I]alpha-BuTX. We report here the use of the protein-blotting technique to detect the alpha-BuTX binding site present in the central nervous system of lower vertebrates and to characterize some of the physicochemical properties of the toxin binding site. High molecular weight (Mr greater than or equal to 200,000 and greater than or equal to 120,000) alpha-BuTX-binding components can be readily demonstrated in avian and fish brain extracts upon protein-blotting with [125I]alpha-BuTX following lithium dodecyl sulfate PAGE. Neither extensive reduction with dithiothreitol nor prior reduction followed by alkylation with iodoacetamide alter the mobility of the CNS-derived BuTX-binding sites. In contrast to our findings with Torpedo AChR or muscle AChR derived from a number of different species, no binding is observed in the molecular weight range of the alpha-subunit (Mr = 40,000) nor is any binding at any molecular weight observed in similar fractions prepared from adult, mammalian (rat, guinea pig) brain using this technique. These results demonstrate the existence in lower vertebrate brain of a BuTX binding site comparable in size to the AChR oligomeric complex of electric organ and muscle. They also suggest, however, striking structural differences between muscle AChR and the central neuronal BuTX-binding complex as well as a considerable difference between the neuronal BuTX-binding sites derived from lower and higher vertebrate brain.

Animals↗

PubMed1986

Binding of rabies virus to purified Torpedo acetylcholine receptor.

The binding of 125I- and 35S-labeled rabies virus (CVS strain) to affinity-purified acetylcholine receptor from Torpedo electric organ was demonstrated. The binding of rabies virus to the acetylcholine receptor increased with increasing receptor concentration, was dependent on the pH of the incubation medium, and was saturable with increasing virus concentration. Binding of radioactively labeled virus was effectively competed by unlabeled homologous virus particles. Binding of 35S-labeled rabies virus to the AChR was inhibited up to 50% by alpha-bungarotoxin and up to 30% by (+)-tubocurarine but was not affected by atropine. These results demonstrate direct binding of rabies virus to a well-defined neurotransmitter receptor, namely the acetylcholine receptor and indicate that at least a portion of the virus interaction occurs near the acetylcholine binding site on the receptor. These findings support the hypothesis that the acetylcholine receptor may serve as a rabies virus receptor in vivo.

Animals↗

PubMed1985

Determination of the primary amino acid sequence specifying the alpha-bungarotoxin binding site on the alpha subunit of the acetylcholine receptor from Torpedo californica.

A region of the alpha subunit of the nicotinic acetylcholine receptor containing the alpha-bungarotoxin-binding domain was mapped on the primary amino acid sequence in relation to asparagine-141, the presumed site of N-linked glycosylation. Proteolytic fragments of the alpha subunit, immobilized onto positively charged membrane filters, that bind 125I-labeled bungarotoxin were further analyzed on the basis of the size of the fragments and the presence of asparagine-141 as determined by susceptibility to digestion with endoglycosidase H. The bungarotoxin-binding site was found not to reside between amino acid residues 1 and 140 since bungarotoxin-binding fragments that are considerably larger than 140 amino acids and lack N-linked oligosaccharide chains were detected. The size of the smallest bungarotoxin-binding fragment containing asparagine-141 and the size of fragments produced by digestion with V8 protease further indicated that the bungarotoxin-binding site is contained within amino acid residues 153-241. A 32-amino acid synthetic peptide comprising a portion of this region (residues 173-204) was tested for its ability to bind 125I-labeled bungarotoxin. 125I-labeled bungarotoxin bound to the peptide and was competed by unlabeled bungarotoxin and d-tubocurarine with IC50 values of 0.5 microM and 2 mM, respectively. We conclude that a major determinant of the bungarotoxin-binding site on the alpha subunit resides between residues 173 and 204.

Amino Acid Sequence↗

PubMed1984

Amino acid sequence similarity between rabies virus glycoprotein and snake venom curaremimetic neurotoxins.

Evidence was presented earlier that a host-cell receptor for the highly neurotropic rabies virus might be the acetylcholine receptor. The amino acid sequence of the glycoprotein of rabies virus was compared by computer analysis with that of snake venom curaremimetic neurotoxins, potent ligands of the acetylcholine receptor. A statistically significant sequence relation was found between a segment of the rabies glycoprotein and the entire sequence of long neurotoxins. The greatest identity occurs with residues considered most important in neurotoxicity, including those interacting with the acetylcholine binding site of the acetylcholine receptor. Because of the similarity between the glycoprotein and the receptor-binding region of the neurotoxins, this region of the viral glycoprotein may function as a recognition site for the acetylcholine receptor. Direct binding of the rabies virus glycoprotein to the acetylcholine receptor could contribute to the neurotropism of this virus.

Amino Acid Sequence↗

PubMed1984

Binding of alpha-bungarotoxin to proteolytic fragments of the alpha subunit of Torpedo acetylcholine receptor analyzed by protein transfer on positively charged membrane filters.

Proteolytic fragments of the alpha subunit of the acetylcholine receptor retain the ability to bind alpha-bungarotoxin following resolution by polyacrylamide gel electrophoresis and immobilization on protein transfers. The alpha subunit of the acetylcholine receptor of Torpedo electric organ was digested with four proteases: Staphylococcus aureus V-8 protease, papain, bromelain, and proteinase K. The proteolytic fragments resolved on 15% polyacrylamide gels were electrophoretically transferred onto positively charged nylon membrane filters. When incubated with 0.3 nM 125I-labeled alpha-bungarotoxin and autoradiographed, the transfers yielded patterns of labeled bands characteristic for each protease. The molecular masses of the fragments binding toxin ranged from 7 to 34 kDa, with major groupings in the 8-, 18-, and 28-kDa ranges. The apparent affinity of the fragments for alpha-bungarotoxin as determined from the IC50 value was 6.7 X 10(-8) M. The labeling of fragments with alpha-bungarotoxin could be inhibited by prior affinity alkylation of receptor-containing membranes with 4-(N-maleimido)-alpha-benzyltrimethylammonium iodide. These findings demonstrate that immobilized proteolytic fragments as small as 1/5 the size of the alpha subunit retain the structural characteristics necessary for binding alpha-bungarotoxin, although the toxin is bound to the fragments with lower affinity than to the native receptor. The effect of affinity ligand alkylation demonstrates that the alpha-bungarotoxin binding site detected on the proteolytic fragments is the same as the affinity-labeled acetylcholine binding site on the intact acetylcholine receptor.

Animals↗

PubMed1979