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Deux fonctions pour une seule protéine ?

Lundi 16 janvier 2006,11h, salle Lissitzky.

Bibliographie

1 : J Cell Sci. 2003 Dec 1 ;116(Pt 23):4751-62.

Specific sorting of the a1 isoform of the V-H+ATPase a subunit to nerve terminals where it associates with both synaptic vesicles and the presynaptic plasma membrane.

Morel N, Dedieu JC, Philippe JM.

Laboratoire de Neurobiologie Cellulaire et Moleculaire, CNRS, 91198 Gif sur Yvette, France. nicolas.morel nbcm.cnrs-gif.fr

Vacuolar H+ATPase (V-ATPase) accumulates protons inside various intracellular organelles, generating the electrochemical proton gradient required for many vital cellular processes. V-ATPase is a complex enzyme with many subunits that are organized into two domains. The membrane domain that translocates protons contains a proteolipid oligomer of several c subunits and a 100 kDa a subunit. Several a-subunit isoforms have been described that are important for tissue specificity and targeting to different membrane compartments, and could also result in the generation of V-ATPases with different functional properties. In the present report, we have cloned the Torpedo marmorata a1 isoform. This isoform was found to be addressed specifically to nerve endings, whereas VATPases in the neuron cell bodies contain a different a-subunit isoform. In nerve terminals, the V-ATPase membrane domain is present not only in synaptic vesicles but also in the presynaptic plasma membrane, where its density could reach 200 molecules microm(-2). This V-ATPase interacts with VAMP-2 and with the SNARE complexes involved in synaptic vesicle docking and exocytosis.


2 : Glia. 2002 Mar 15 ;37(4):365-73

Functional expression of V-ATPases in the plasma membrane of glial cells.

Philippe JM, Dubois JM, Rouzaire-Dubois B, Cartron PF, Vallette F, Morel N.

Laboratoire de Neurobiologie Cellulaire et Moleculaire, CNRS, Gif sur Yvette, France.

Vacuolar H(+) ATPase (V-ATPase) activity is essential for many cellular processes, including intracellular membrane traffic, protein processing and degradation, and receptor-mediated endocytosis. Proton transport by V-ATPases could also play a role during cell transformation, tumorigenesis, and cell metastasis, and V-ATPase c-subunit overexpression was reported to be correlated with invasiveness of pancreatic tumors (Ohta et al., 1996). In the present work, we found that mRNAs encoding V-ATPase subunits are not overexpressed in C6 tumoral glioma cells when compared with immortalized astrocytes DI TNC1 and astrocytes in primary cultures. Accordingly, V-ATPase subunit mRNA levels are similar in human gliomas (grade II or IV) and in peritumoral tissues. A significant proportion (25%) of V-ATPase is present in the plasma membrane of both the C6 and the DI TNC1 astrocytic cells in culture. A bafilomycin-sensitive hyperpolarizing pump current through the plasma membrane was detected and measured after ionic channel inhibition, which corresponds most probably to an electrogenic transport of protons. This suggests that the plasma membrane V-ATPase is active. It could contribute to cytoplasmic pH regulation in astrocytic cells. Copyright 2002 Wiley-Liss, Inc.


3 : J Neurochem. 2001 Nov ;79(3):485-8.

Neurotransmitter release through the V0 sector of V-ATPase.

Morel N, Dunant Y, Israel M.

Laboratoire de Neurobiologie Cellulaire et Moleculaire, CNRS, Gif sur Yvette, France. nicolas.morel nbcm.cnrs-gif.fr

Publication Types : Review


4 : J Biol Chem. 2001 Oct 5 ;276(40):37379-89. Epub 2001 Jul 6.

Acetylcholinesterase H and T dimers are associated through the same contact. Mutations at this interface interfere with the C-terminal T peptide, inducing degradation rather than secretion.

Morel N, Leroy J, Ayon A, Massoulie J, Bon S.

Laboratoire de Neurobiologie Cellulaire et Moleculaire, CNRS UMR 8544, Ecole Normale Superieure, 46 rue d’Ulm, 75005 Paris, France.

Acetylcholinesterase (AChE) exists as AChE(H) and AChE(T) subunits, which differ by their C-terminal H or T peptides, generating glycophosphatidylinositol-anchored dimers and various oligomers, respectively. We introduced mutations in the four-helix bundle interface of glycophosphatidylinositol-anchored dimers, and analyzed their effect on the production and oligomerization of AChE(H), of AChE(T), and of truncated subunits, AChE(C) (without H or T peptide). Dimerization was reduced for all types of subunits, showing that they interact through the same contact zone ; the formation of amphiphilic tetramers (Torpedo AChE(T)) and 13.5 S oligomers (rat AChE(T)) was also suppressed. Oligomerization appeared totally blocked by introduction of an N-linked glycan on the surface of helix alpha(7,8). Other point mutations did not affect the synthesis or the catalytic properties of AChE but reduced or blocked the secretion of AChE(T) subunits. Secretion of AChE(T) was partially restored by co-expression with Q(N), a secretable protein containing a proline-rich attachment domain (PRAD) ; Q(N) organized PRAD-linked tetramers, except for the N-glycosylated mutants. Thus, the simultaneous presence of an abnormal four-helix bundle zone and an exposed T peptide targeted the enzyme toward degradation, indicating a cross-talk between the catalytic and tetramerization domains.


5 : Biol Cell. 2003 Oct ;95(7):453-7.

Neurotransmitter release : the dark side of the vacuolar-H+ATPase.

Morel N.

Laboratoire de Neurobiologie Cellulaire et Moleculaire, CNRS, 91198 Gif sur Yvette, France. nicolas.morel nbcm.cnrs-gif.fr

Vacuolar-H+ATPase (V-ATPase) is a complex enzyme with numerous subunits organized in two domains. The membrane domain V0 contains a proteolipid hexameric ring that translocates protons when ATP is hydrolysed by the catalytic cytoplasmic sector (V1). In nerve terminals, V-ATPase generates an electrochemical proton gradient that is acid and positive inside synaptic vesicles. It is used by specific neurotransmitter-proton antiporters to accumulate neurotransmitters inside their storage organelles. During synaptic activity, neurotransmitters are released from synaptic vesicles docked at specialized portions of the presynaptic plasma membrane, the active zones. A fusion pore opens that allows the neurotransmitter to be released from the synaptic vesicle lumen into the synaptic cleft. We briefly review experimental data suggesting that the membrane domain of V-ATPase could be such a fusion pore. We also discuss the functional implications for quantal neurotransmitter release of the sequential use of the same V-ATPase membrane domain in two different events, neurotransmitter accumulation in synaptic vesicles first, and then release from these organelles during synaptic activity.

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