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Y Maulet

Publications and source records attributed to Y Maulet.

24 records · Page 2Linked to original sources
PubMed1984

Selective solubilization by melittin of glycophorin A and acetylcholinesterase from human erythrocyte ghosts.

Melittin, the main basic and hydrophobic peptide of bee venom, has been used for solubilizing membrane components of the human erythrocyte ghost. Up to 1.0 mM, it does not extract any phospholipid. Between 0.1 and 1.0 mM, it solubilizes partially glycophorin A and acetylcholinesterase. When the membrane is first degraded by phospholipase A2, the solubilization of both proteins by melittin is total, and 48% of the phospholipids are removed, mainly as lysoproducts, whereas phospholipase A2, by itself, has no solubilizing properties. In its melittin-solubilized state, acetylcholinesterase is in a dimeric form and displays a slow time-dependent irreversible inactivation. Triton X-100 at 1.0% (v/v) interrupts the inactivation. We suggest that melittin binds to the hydrophobic site of acetylcholinesterase which anchors it in the lipid bilayer.

Acetylcholinesterase↗
PubMed1983

Structural changes in melittin and calmodulin upon complex formation and their modulation by calcium.

In the presence of Ca2+, calmodulin forms a 1:1 high-affinity complex (Kd = 3 nM) with melittin, a peptide from bee venom; in the presence of ethylenediaminetetraacetic acid, a second type of complex, of much lower affinity, is formed [Comte, M., Maulet, Y., & Cox, J. A. (1983) Biochem. J. 209, 269-272]. In this paper, these interactions were studied by tryptophan fluorescence and circular dichroism spectroscopy in near- and far-UV. Interaction between the two peptides in the presence as well as in the absence of Ca2+ leads to the shielding of the tryptophan residue of melittin from its aqueous environment and to an increase in the alpha-helical content of bound melittin; for instance the Ca2+-dependent high-affinity complex formation enhances the alpha-helical content of melittin from 5 to 72%. Provided Ca2+ is present, the interaction between the two peptides leads to significant changes in the environment of at least one tyrosine residue of calmodulin as measured by near-UV circular dichroism. In the absence of Ca2+, calmodulin binds two melittin molecules with a Kd of ca. 10 microM; at higher concentrations of free melittin, additional binding occurs (up to 5 mol of melittin/mol of calmodulin), with concomitant denaturation of calmodulin. In the presence of 4.0 M urea, the low-affinity complexes formed in the absence of Ca2+ dissociate, due to the denaturation of metal-free calmodulin, whereas the spectroscopic signals of the high-affinity Ca2+-dependent complex are not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Ca2+-dependent high-affinity complex formation between calmodulin and melittin.

The amphiphatic polypeptide melittin migrates as an equimolar complex with bovine brain calmodulin when monitored by gel disc electrophoresis or gel filtration in the presence of Ca2+, even in 4M-urea. The complex disassociates in the presence of EDTA and urea. The affinity is of the same order as that of calmodulin for its target enzymes, and more than 1000-fold higher than that of calmodulin for basic peptide hormones or hydrophobic drugs. The activation of brain phosphodiesterase by calmodulin is inhibited by melittin. The kinetics of inhibition suggest competition between the enzyme and melittin for calmodulin. The calmodulin-melittin interaction may constitute a model for that existing between calmodulin and its target enzymes.

Animals↗
PubMed1980

Purification and chemical characterization of melittin and acetylated derivatives.

Melittin, the main basic and hydrophobic peptide of bee venom, displays marked detergent-like properties. At high peptide concentration, and depending on salt and pH, it forms a tetramer. This is prevented by using urea. A purification procedure in presence of 4.0 M urea was developed to prepare melittin in its monomeric form, free of other venom constituents such as N alpha-formyl melittin, degradation products of peptides and phospholipase A2. NH2-residues on the melittin molecule were modified by reaction with acetic anhydride to alter the asymmetrical charge distribution supposed to confer detergent-like properties to the molecule. This gave rise to di- and mono acetyl derivatives which could be used, once isolated, to study further the melittin structure-activity relationship.

Animals↗
PubMedDate not supplied

Primary structure of Torpedo californica acetylcholinesterase deduced from its cDNA sequence.

Acetylcholinesterase, an essential enzyme of the nervous system, rapidly terminates the action of acetylcholine released into the synapse. Acetylcholinesterase is also found (in lower abundance) in extrajunctional areas of muscle and nerve and on erythrocyte membranes. Hydrodynamic analyses of the native enzyme and characterization of its dissociated subunits have revealed multiple enzyme forms which can be divided into two classes: dimensionally asymmetric forms which are usually found within the synapse and contain a collagen-like structural subunit disulphide-linked to the catalytic subunits; and globular forms which appear to be widely distributed on the outer surface of cell membranes. Both forms have been characterized in the ray Torpedo californica and, although their catalytic behaviours seem to be identical, they differ slightly in amino-acid composition, peptide maps and reactivity with certain monoclonal antibodies. Here, we report the complete amino-acid sequence of an acetylcholinesterase inferred from the sequence of a complementary DNA clone. The 575-residue protein shows significant homology with the C-terminal portion of thyroglobulin.

Acetylcholinesterase↗