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B M Conti-Tronconi

Publications and source records attributed to B M Conti-Tronconi.

84 records · Page 5Linked to original sources
PubMed1982

Mammalian muscle acetylcholine receptor purification and characterization.

Nicotinic acetylcholine receptor (AcChR) was purified from fetal calf muscle by an affinity chromatographic method utilizing alpha-neurotoxin from Naja naja siamensis as an immobilized ligand. Preparations of AcChR with an average specific activity of 5 nmol of alpha-toxin bound/mg of protein were obtained, i.e., 75% of the theoretical specific activity assuming identity with Torpedo AcChR. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified AcChR consistently showed the presence of five polypeptides, having apparent Mr's of 42 000, 44 000, 49 000, 55 000, and 58 000, respectively. The peptide of Mr 44K was demonstrated to be actin. The amino acid composition of fetal calf AcChR was shown to be similar to that of Torpedo AcChR. In addition, calf AcChR contained large amounts of amino sugars. The sedimentation coefficient of the purified calf AcChR was found to be 9.25 +/- 0.25, i.e., similar to the monomeric form of electric organ AcChR. Determination of the isoelectric point of alpha-bungarotoxin/calf AcChR complexes revealed the presence of two charged forms, having pI values of 5.16 +/- 0.13 and 6.05 +/- 0.18, respectively.

Amino Acids↗
PubMed1982

Functional stability of Torpedo acetylcholine receptor. Effects of protease treatment.

The effect of tryptic degradation on structural and functional properties of the membrane-bound acetylcholine receptor from Torpedo californica has been investigated. Under conditions of proteolysis which resulted in extensive degradation of receptor subunits, the membrane preparations retained their full capability of mediating agonist-induced cation flux as measured in rapid kinetic experiments. Low concentrations on trypsin also cleaved receptor dimers to monomers, and this effect was paralleled by degradation of the Mr 65 000 subunits which are known to contain sulfhydryl group(s) involved in receptor dimerization through an interchain disulfide bond(s). This conversion to monomers occurred at lower trypsin concentrations when the enzyme was added to the outside of the vesicles compared with the effects observed when the enzyme was present inside the vesicles. Similarly Mr 43 000 protein consistently found in preparations of the membrane-bound acetylcholine receptor, which can readily be removed without apparent effect on receptor function, displayed greater susceptibility to proteolysis when trypsin was added to the exterior medium rather than inside the vesicles. The results emphasize the full functionality of the monomeric form of the acetylcholine receptor comprised of four polypeptides.

Animals↗
PubMed1982

Subunit structure of the acetylcholine receptor from Electrophorus electricus.

The amino-terminal amino acid sequences of the four major peptides (Mr 41,000, 50,000, 55,000, and 62,000) present in purified preparations of Electrophorus electricus nicotinic acetylcholine receptor (AcChoR) have been determined for 24 cycles by automated sequence analysis procedures yielding four unique polypeptide sequences. The sequences showed a high degree of similarity, having identical residues in a number of positions ranging between 37% and 50% for specific pairs of subunits. Comparison of the sequences obtained with those of the subunits of similar molecular weight from Torpedo californica AcChoR revealed an even higher degree of homology (from 46% to 71%) for these two highly diverged species. Simultaneous sequence analysis of the amino termini present in native, purified Electrophorus AcChoR showed that these four related sequences were the only ones present and that they occur in a ratio of 2:1:1:1, with the smallest subunit ("alpha 1") being present in two copies. Genealogical analysis suggests that the subunits of both Torpedo and Electrophorus AcChoRs derive from a common ancestral gene, the divergence having occurred early in the evolution of the receptor. This shared ancestry and the very early divergence of the four subunits, as well as the highly conserved structure of the AcChoR complex along animal evolution, suggest that each of the subunits evolved to perform discrete crucial roles in the physiological function of the AcChoR.

Amino Acid Sequence↗
PubMed1979

Cellular immune response against acetylcholine receptor in myasthenia gravis: I. Relevance to clinical course and pathogenesis.

The cellular immune response to acetylcholine receptor from Torpedo electric organ was studied in 100 myasthenic patients and 41 healthy subjects. The mean stimulation index (SI) was 2 +/- 0.15 for the patients, and 1.06 +/- 0.08 for the controls. Stimulation was significantly greater when the test medium contained autologous serum rather than a standard universal serum (AB serum). Young patients were generally good responders (SI, 2.39 +/- 0.26), but older patients usually did not respond (mean SI, 1.18 +/- 0.13). Among the younger patients, men had higher responses than women (mean SI, 3.13 +/- 0.63 and 2.05 +/- 0.23, respectively). There was no correlation between degree of lymphocytic reactivity and duration or severity of symptoms.

Acetylcholine↗
PubMed1979

Cellular immune response to acetylcholine receptor in myasthenia gravis: II. Thymectomy and corticosteroids.

We studied 11 patients with myasthenia gravis who demonstrated a cellular immune response to acetylcholine receptor (AChR) of the electric organ of Torpedo marmorata. After thymectomy, there was a marked decrease in the patients' lymphocyte reactivity to AChR. The mean reduction of the stimulation index (SI) was 50%, but the response to the nonspecific mitogen phytohemagglutinin (PHA) was not affected. In six cases, the lymphocyte response was measured at intervals up to 22 months after thymectomy; in all six, the immune response to AChR remained decreased. In some cases, the response continued to decrease, even to normal values. The effect of corticosteroid treatment was tested in other patients. The cellular immune response to AChR was significantly lower in treated patients (mean SI, 1.64 +/- 0.25) than in untreated controls (mean SI, 2.41 +/- 0.38), with no significant difference in the response to PHA. These data suggest that a decrease in the cellular immune response to AChR may be one mechanism by which thymectomy and corticosteroids are therapeutic in myasthenia.

Acetylcholine↗
PubMed1978

Lymphocyte stimulation by acetylcholine receptor in polymyositis.

Lymphocytes of twenty-seven patients with polymyositis were incubated in vitro with cholinergic receptor rich membranes obtained from the electric organs of Torpedo Marmorata. Lymphocytes of polymyositic patients were slightly stimulated; positive responses were present mainly in patients affected from more than a year. Sensitization against the nicotinic cholinergic receptor may explain the occurrence of the myasthenic syndrome with polymyositis.

Animals↗
PubMed1977

Stimulation of lymphocytes by cholinergic receptor in myasthenia gravis.

Lymphocytes from 13 myasthenic patients were incubated in vitro with membranes enriched in nicotinic cholinergic receptor obtained from Torpedo marmorata electric organ. When autologous serum was present in the incubation medium, the lymphocytes were highly stimulated. In contrast, no stimulation occurred when lymphocytes were cultured in presence of AB serum. These results suggest that an immune response against the Ach cholinergic receptor is present in myasthenic patients and give further support to the hypothesis that an autoimmune response against muscular receptors may be involved in Myasthenia Gravis pathogenesis.

Adult↗
PubMedDate not supplied

Adult thymus expresses an embryonic nicotinic acetylcholine receptor-like protein.

The subunit composition of acetylcholine receptor-like protein(s) (AChR-LP) expressed by normal thymus was investigated. In skeletal muscle, the AChR exists in two forms, an embryonic form which contains the gamma-subunit and an adult form where the gamma-subunit is substituted by a different, homologous subunit called epsilon. Antibodies against unique sequence segments of the embryonic gamma-subunit and of the adult epsilon-subunit of bovine muscle AChR, in addition to antibodies specific for the alpha-, beta-, and delta-subunits of bovine muscle AChR, were used to probe immunoblots of AChR-LP(s) from bovine thymus. Subunits of approximate Mr 41 kDa, 48-54 kDa, 57 kDa and 67-72 kDa were recognized by anti-alpha, anti-beta, anti-gamma and anti-delta antibodies respectively. Anti-epsilon antibodies did not recognize any protein band from bovine thymus. AChR-LP similar or identical to the embryonic muscle AChR is therefore expressed in normal thymus.

Amino Acid Sequence↗