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A Anselmet

Publications and source records attributed to A Anselmet.

14 recordsLinked to original sources
PubMed1999

The polymorphism of acetylcholinesterase: post-translational processing, quaternary associations and localization.

The molecular forms of acetylcholinesterase (AChE) correspond to various quaternary structures and modes of anchoring of the enzyme. In vertebrates, these molecules are generated from a single gene: the catalytic domain may be associated with several types of C-terminal peptides, that define distinct types of catalytic subunits (AChE(S), AChE(H), AChE(T)) and determine their post-translational maturation. AChE(S) generates soluble monomers, in the venom of Elapid snakes. AChE(H) generates GPI-anchored dimers, in Torpedo muscles and on mammalian blood cells. AChE(T) is the only type of catalytic subunit that exists in all vertebrate cholinesterases; it produces the major forms in adult brain and muscle. AChE(T) generates multiple structures, ranging from monomers and dimers to collagen-tailed and hydrophobic-tailed forms, in which catalytic tetramers are associated with anchoring proteins that attach them to the basal lamina or to cell membranes. In the collagen-tailed forms, AChE(T) subunits are associated with a specific collagen, ColQ, which is encoded by a single gene in mammals. ColQ contains a short peptidic motif, the proline-rich attachment domain (PRAD), that triggers the formation of AChE(T) tetramers, from monomers and dimers. The critical feature of this motif is the presence of a string of prolines, and in fact synthetic polyproline shows a similar capacity to organize AChE(T) tetramers. Although the COLQ gene produces multiple transcripts, it does not generate the hydrophobic tail. P, which anchors AChE in mammalian brain membranes. The coordinated expression of AChE(T) subunits and anchoring proteins determines the pattern of molecular forms and therefore the localization and functionality of the enzyme.

Acetylcholinesterase↗
PubMed1994

Evolution of acetylcholinesterase transcripts and molecular forms during development in the central nervous system of the quail.

We studied the expression of acetylcholinesterase (AChE) in the nervous system (cerebellum, optic lobes and neuroretina) of the quail at different stages of development, from embryonic day 10 (E10) to the adult. Analyzing AChE mRNAs and AChE molecular forms, we observed variations in the following: (a) production of multiple mRNA species (4.5 kb, 5.3 kb, and 6 kb); (b) translation and/or stability of the AChE protein; (c) production of active and inactive AChE molecules; (d) production of amphiphilic and nonamphiphilic AChE forms; and (e) proportions of tetrameric G4, dimeric G2, and monomeric G1 forms. The large transcripts present distinct temporal patterns and disappear in the adult, which possesses only the 4.5-kb mRNA; these changes are unlikely to be related to those observed for the AChE protein, because all transcripts seem to encode the same catalytic subunit (type T). In addition, the levels of mRNA and AChE are not correlated in the three regions, especially at the adult stage. The proportion of inactive AChE was found to be markedly higher at the hatching period (E16) than at earlier stages (E10 and E13) or in the adult. The G4 form is predominant already at E10, and in the adult its proportion reaches 80% of the activity in the cerebellum and optic lobes, and 65-70% in the neuroretina. This form is largely nonamphiphilic in embryonic tissues, but it becomes progressively more amphiphilic with development. Thus, the different processing and maturation steps appear to be regulated in an independent manner and potentially correspond to physiologically adaptative mechanisms.

Acetylcholinesterase↗
PubMed1988

Complex alternative splicing of acetylcholinesterase transcripts in Torpedo electric organ; primary structure of the precursor of the glycolipid-anchored dimeric form.

In this paper, we show the existence of alternative splicing in the 3' region of the coding sequence of Torpedo acetylcholinesterase (AChE). We describe two cDNA structures which both diverge from the previously described coding sequence of the catalytic subunit of asymmetric (A) forms (Schumacher et al., 1986; Sikorav et al., 1987). They both contain a coding sequence followed by a non-coding sequence and a poly(A) stretch. Both of these structures were shown to exist in poly(A)+ RNAs, by S1 mapping experiments. The divergent region encoded by the first sequence corresponds to the precursor of the globular dimeric form (G2a), since it contains the expected C-terminal amino acids, Ala-Cys. These amino acids are followed by a 29 amino acid extension which contains a hydrophobic segment and must be replaced by a glycolipid in the mature protein. Analyses of intact G2a AChE showed that the common domain of the protein contains intersubunit disulphide bonds. The divergent region of the second type of cDNA consists of an adjacent genomic sequence, which is removed as an intron in A and Ga mRNAs, but may encode a distinct, less abundant catalytic subunit. The structures of the cDNA clones indicate that they are derived from minor mRNAs, shorter than the three major transcripts which have been described previously (14.5, 10.5 and 5.5 kb). Oligonucleotide probes specific for the asymmetric and globular terminal regions hybridize with the three major transcripts, indicating that their size is determined by 3'-untranslated regions which are not related to the differential splicing leading to A and Ga forms.

Amino Acid Sequence↗
PubMed1985

Triiodothyronine nuclear receptor and the role of non-histone protein factors in in vitro triiodothyronine binding.

The rat liver triiodothyronine (T3) nuclear receptor rapidly looses, after a partial purification from the nuclear extract, its ability to bind T3. We previously reported that histones, in the presence of DNA, could protect against inactivation enhancing the T3 binding site concentration and maintaining the high affinity for T3. A nuclear fraction discarded during the receptor purification (fraction A) was also found able to restore T3 binding and was analyzed. As histones + DNA, fraction A stabilized the T3 binding site from irreversible inactivation during incubation with T3, increasing its concentration while keeping the same high affinity for T3. It was active even at relatively high receptor concentration, appeared slightly more active than histones (+ DNA) in the same protein concentration range (up to 50-fold increment of T3 binding at the optimal concentration of 25 micrograms/ml) and was unaffected or slightly inhibited by DNA. Other proteins (ovalbumin, soybean trypsin inhibitor, RNAase) and rat liver cytosol were several times less effective, suggesting a major role of some nuclear constituents. The active factors in fraction A essentially belong to non-histone nuclear proteins. Fraction A was found heterogeneous regarding the molecular size and pHi of the active factors, the existence of subfractions more active on a protein concentration basis being suggested but not yet clearly evidenced. Efficient in vitro T3 binding to the isolated T3 nuclear receptor thus depends on the presence of several different nuclear constituents, histones + DNA or some non-histone proteins. Whether interactions with these constituents could modulate T3 binding within the nucleus remains to be elucidated.

Animals↗
PubMed1984

Nuclear triiodothyronine receptor in differentiating preadipocytes cloned from obese and lean mice.

The nuclear T3 receptor was characterized in two T3-responsive preadipocyte cell lines cloned from the epididymal fat pads of ob/ob adult mice (ob 17 cells) and their lean counterpart (HGFu cells). Isolated nuclei from confluent or differentiating cells bound [125I]T3 to one class of high affinity sites exhibiting kinetic properties, stereospecificity, and salt extractibility of the nuclear T3 receptor. The solubilized T3 binding sites behave like the hepatic nuclear T3 receptor considering physicochemical and DNA binding properties. At confluence, no significant difference could be detected in equilibrium apparent affinity constant (Ka) and maximum binding capacity (MBC) for T3 whether nuclei were prepared from cells originating from ob/ob mice [Ka: 1.7 +/- (SE) 0.5 X 10(10) M-1; MBC: 432 +/- 29 fmol/mg DNA] or from lean mice (Ka: 1.6 +/- 0.2 X 10(10) M-1; MBC: 487 +/- 39 fmol/mg DNA). MBC values were in the range found in several T3-responsive tissues. This suggests that the primary defect in ob/ob mice is probably not at the level of the nuclear T3 receptor. Furthermore, during differentiation into adipose cells in both cell series, and roughly paralleling the amplifying effect of T3 on several lipogenic enzymes in the course of their development, the nuclear T3 receptor concentration significantly increased, attaining about twice the initial values after completion of the differentiation without any significant change in the affinity for T3.

Adipose Tissue↗
PubMed1984

[Changes in the nuclear triiodothyronine receptor during the differentiation of preadipocytic cell lines of mice].

During the differentiation process of ob 17 preadipocytes in the presence of insulin, a progressive increase in the nuclear T3 receptor concentration per cell (1.5 to 3 fold) was observed. This increase was not found related to the addition of insulin to the culture medium and was concomitant to the expression of several phenotypes of the mature adipocyte. Triiodothyronine (T3) added to the culture medium of these cells increases the lipogenic pathway and several enzymes involved in fatty acid synthesis and esterification. After T3 addition at the same optimal physiologic concentration of 1.5 nM, the cellular concentration of its nuclear receptor was clearly reduced, without any significant alteration in the apparent affinity constant. A similar behavior was observed in 3T3-L1 preadipocytes. The molecular mechanism of action of the T3 nuclear receptor within the chromatin is not known. The biological relevance of its depletion by T3 itself remains to be determined.

Adipose Tissue↗
PubMed1983

Triiodothyronine nuclear receptor. Role of histones and DNA in hormone binding.

The triiodothyronine (T3) nuclear receptor was previously shown to lose rapidly its high affinity hormone-binding property after a partial purification from the nuclear extract. It was then found that histones + DNA added to the incubation medium with labeled T3 could restore, at least in part, the high affinity T3 binding. We now demonstrate that DNA alone increases the high affinity T3 binding site concentration moderately, and only at low ionic strength where it can bind to the receptor. Total histones and all histone fractions studied (total core histones, F2a, H2B, H3, H4, H1) specifically increase, at low concentrations, the level of T3 binding; but higher concentrations of some individualized histones, particularly arginine-rich histones, have an inhibitory effect. DNA, or several other polynucleotides, in the presence of histones increase the stimulating histone effect and reverse the inhibitory effect into a true activation. Histones increase the number of T3 binding sites but decrease the affinity for T3; addition of DNA restores the high affinity for T3 and stabilizes the T3-receptor complexes. Thus, some of the histone molecules could play a role in the maintenance of the T3 binding site, but multiple interactions between histones or with DNA seem necessary to impair the negative effect exerted by other parts of the histone molecules. Whether these positive and negative effects of histones on the T3 binding site are of biological relevance in the regulation of T3 binding to its receptor remains to be determined.

Animals↗
PubMed1978

Properties of solubilized nuclear triiodothyronine binding proteins.

Rat liver nuclear proteins bind 3,5,3'-triiodo-L-thyronine (T3) to essentially one class of sites (Ka approximately 1 X 10(10) M-1). Gel filtration and sucrose gradient centrifugation studies show a main T3 binding component with a Stokes radius of 33 A and a sedimentation coefficient of 3.5S, and variable amounts of high molecular weight binding components, most of them being reversible aggregates of the main component formed during storage. But the uniqueness of the nuclean T3 binding proteins (NTBP) cannot be ascertained from polyacrylamide gel electrophoresis data. During storage in the absence of reducing agents, NTBP aggregate and rapidly lose their ability to bind T3; T3--NTBP complexes also aggregate and progressively dissociate. This can be reversed by dithiothreitol. Bound T3 could temporarily stabilize the binding site but cannot protect NTBP against general conformational changes which follow the oxidation of their essential --SH group(s). NTBP are DNA binding proteins with probably a relative independence of their DNA and T3 binding sites: they bind T3 to the same class of high affinity sites whether complexed or not with DNA; bound T3 is not a prerequisite for DNA binding.

Animals↗
PubMedDate not supplied

Acetylcholinesterase: C-terminal domains, molecular forms and functional localization.

Acetylcholinesterase (AChE) possesses short C-terminal peptides that are not necessary for catalytic activity. These peptides belong to different classes (R, H, T, S) and define the post-translational processing and targeting of the enzyme. In vertebrates, subunits of type H (AChEH) and of type T (AChET) are the most important: AChEH subunits produce glycolipid (GPI)-anchored dimers and AChET subunits produce hetero-oligomeric forms such as membrane-bound tetramers in the mammalian brain (containing a 20 kDa hydrophobic protein) and asymmetric collagen-tailed forms in neuromuscular junctions (containing a specific collagen, ColQ). The T peptide allows the formation of tetrameric assemblies with a proline-rich attachment domain (PRAD) of collagen ColQ. These complex molecular structures condition the functional localization of the enzyme in the supramolecular architecture of cholinergic synapses.

Acetylcholinesterase↗