Defining the functional role of NaV1.7 in human nociception

Loss-of-function mutations in NaV1.7 cause congenital insensitivity to pain (CIP); this voltage-gated sodium channel is therefore a key target for analgesic drug development. Utilizing a multi-modal approach, we investigated how NaV1.7 mutations lead to human pain insensitivity. Skin biopsy and microneurography revealed an absence of C-fiber nociceptors in CIP patients, reflected in a reduced cortical response to capsaicin on fMRI. Epitope tagging of endogenous NaV1.7 revealed the channel to be localized at the soma membrane, axon, axon terminals, and the nodes of Ranvier of induced pluripotent stem cell (iPSC) nociceptors. CIP patient-derived iPSC nociceptors exhibited an inability to properly respond to depolarizing stimuli, demonstrating that NaV1.7 is a key regulator of excitability. Using this iPSC nociceptor platform, we found that some NaV1.7 blockers undergoing clinical trials lack specificity. CIP, therefore, arises due to a profound loss of functional nociceptors, which is more pronounced than that reported in rodent models, or likely achievable following acute pharmacological blockade

Relations structure - fonction des transporteurs mitochondriaux

The Mitochondrial Carrier Family (MCF) groups integral membrane proteins that transport various metabolites across the inner mitochondrial membrane. This transport is needed in major metabolic pathways occurring in mitochondria and is essential in eukaryotic metabolism. The mis-function of several identified human mitochondrial carriers has been associated with severe diseases. In order to achieve a better understanding of mitochondrial carriers two different families of mitochondrial carriers where chosen to be studied: the AACs (ADP/ATP Carriers) and the UCPs (UnCoupling Proteins). Two heterologous expression systems of these carriers were developed: the cell free and the expression in E. coli as fusion proteins. The cell free system allowed the production and purification of about 0,6 mg of protein per milliliter of reaction mixture and the expression in E.coli proved to be very efficient for the functional characterization of ADP/ATP carriers. A functional test was developed for the uncoupling protein also. This test, based on the measure of electrical currents generated by the transport activity of UCP, allowed the functional characterization of native UCP1.Le passage sélectif d'ions et de métabolites à travers les membranes biologiques est essentiel à de nombreux processus cellulaires fondamentaux. Au niveau de la membrane interne de la mitochondrie, la communication cellulaire et les processus d'échanges sont principalement assurés par les transporteurs mitochondriaux. Ces protéines membranaires jouent un rôle clef dans les fonctions métaboliques des cellules eucaryotes et leur dysfonctionnement est à l'origine d'un certain nombre de maladies graves chez l'homme Parmi les transporteurs mitochondriaux, deux familles ont été étudiées au cours de ce travail : les AACs (ADP/ATP Carriers) et les UCPs (UnCoupling Proteins). Deux systèmes de production hétérologue de ces transporteurs ont été mis en place : la synthèse in vitro et l'expression chez E. coli de protéines de fusion. Le premier a permis la production et la purification d'environ 0,6 mg de protéine par mL de réaction et le deuxième a été exploité afin de réaliser des caractérisations fonctionnelles des transporteurs ADP/ATP. Un test fonctionnel pour la protéine découplante a également été mis au point. Ce test, basé sur la mesure directe des courants électriques associés à l'activité de transport de l'UCP, à permis la caractérisation fonctionnelle de la protéine UCP1 native

Relations structure - fonction des transporteurs mitochondriaux

The Mitochondrial Carrier Family (MCF) groups integral membrane proteins that transport various metabolites across the inner mitochondrial membrane. This transport is needed in major metabolic pathways occurring in mitochondria and is essential in eukaryotic metabolism. The mis-function of several identified human mitochondrial carriers has been associated with severe diseases. In order to achieve a better understanding of mitochondrial carriers two different families of mitochondrial carriers where chosen to be studied: the AACs (ADP/ATP Carriers) and the UCPs (UnCoupling Proteins). Two heterologous expression systems of these carriers were developed: the cell free and the expression in E. coli as fusion proteins. The cell free system allowed the production and purification of about 0,6 mg of protein per milliliter of reaction mixture and the expression in E.coli proved to be very efficient for the functional characterization of ADP/ATP carriers. A functional test was developed for the uncoupling protein also. This test, based on the measure of electrical currents generated by the transport activity of UCP, allowed the functional characterization of native UCP1.Le passage sélectif d'ions et de métabolites à travers les membranes biologiques est essentiel à de nombreux processus cellulaires fondamentaux. Au niveau de la membrane interne de la mitochondrie, la communication cellulaire et les processus d'échanges sont principalement assurés par les transporteurs mitochondriaux. Ces protéines membranaires jouent un rôle clef dans les fonctions métaboliques des cellules eucaryotes et leur dysfonctionnement est à l'origine d'un certain nombre de maladies graves chez l'homme Parmi les transporteurs mitochondriaux, deux familles ont été étudiées au cours de ce travail : les AACs (ADP/ATP Carriers) et les UCPs (UnCoupling Proteins). Deux systèmes de production hétérologue de ces transporteurs ont été mis en place : la synthèse in vitro et l'expression chez E. coli de protéines de fusion. Le premier a permis la production et la purification d'environ 0,6 mg de protéine par mL de réaction et le deuxième a été exploité afin de réaliser des caractérisations fonctionnelles des transporteurs ADP/ATP. Un test fonctionnel pour la protéine découplante a également été mis au point. Ce test, basé sur la mesure directe des courants électriques associés à l'activité de transport de l'UCP, à permis la caractérisation fonctionnelle de la protéine UCP1 native

Relations structure - fonction des transporteurs mitochondriaux

Le passage sélectif d'ions et de métabolites à travers les membranes biologiques est essentiel à de nombreux processus cellulaires fondamentaux. Au niveau de la membrane interne de la mitochondrie, la communication cellulaire et les processus d'échanges sont principalement assurés par les transporteurs mitochondriaux. Ces protéines membranaires jouent un rôle clef dans les fonctions métaboliques des cellules eucaryotes et leur dysfonctionnement est à l'origine d'un certain nombre de maladies graves chez l'homme Parmi les transporteurs mitochondriaux, deux familles ont été étudiées au cours de ce travail: les AACs (ADP/A TI Carriers) et les UCPs (UnCoupling Proteins). Deux systèmes de production hétérologue de ces transporteurs ont été mil en place: la synthèse in vitro et l'expression chez E.coli de protéines de fusion. Le premier a permis la production et 1 purification d'environ 0,6 mg de protéine par mL de réaction et le deuxième a été exploité afin de réaliser dl caractérisations fonctionnelles des transporteurs ADP/ATP. Un test fonctionnel pour la protéine découplante a égalemel été mis au point. Ce test, basé sur la mesure directe des courants électriques associés à l'activité de transport de l'UCP, permis la caractérisation fonctionnelle de la protéine UCPI native.The Mitochondrial Carrier Family (MCF) groups integral membrane proteins that transport various metabolites across, the inner mitochondrial membrane. This transport is needed in major metabolic pathways occurring in mitochondria and is essential in eukaryotic metabolism. The mis-function of several identified human mitochondrial carriers has been associated with severe diseases . ln order to achieve a better understanding of mitochondrial carriers two different families of mitochondrial carriers where chosen to be studied: the AACs (ADP/ATP Carriers) and the UCPs (UnCoupling Proteins). Two heterologous expression systems of these carriers were developed: the cell free and the expression in E. coli as fusion proteins. The cell free system allowed the production and purification of about 0,6 mg of protein per milliliter of reaction mixture and the expression in E.coli proved to be very efficient for the functional characterization of ADPI A TP carriers. A functional test was developed for the uncoupling protein also. This test, based on the measure of electrical currents generated by the transport activity ofUCP, allowed the functional characterization of native UCPI.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Single-step production of functional OEP24 proteoliposomes.

International audienceThe pea chloroplastic outer envelope protein OEP24 is a voltage-dependent channel that can function as a general solute channel in plants. OEP24 is a close functional homologue of VDAC which, in mammalian cells, modulates the permeability of the outer mitochondrial membrane. Here, we describe the production in a one-step reaction of active OEP24 in proteoliposomes or in soluble form using a cell-free expression system. We combine evidence from electrophysiological experiments, biophysical characterization, and biochemical analysis demonstrating that OEP24 is present as a functional channel in liposomes. Thus, production of OEP-containing proteoliposomes may provide a helpful tool for deciphering the role of the OEP family members

Crystallization of the membrane protein hVDAC1 produced in cell-free system.

International audienceStructural studies of membrane proteins are in constant evolution with the development of new improvements for their expression, purification, stabilization and crystallization. However, none of these methods still provides a universal approach to solve the structure of membrane proteins. Here we describe the crystallization of the human voltage-dependent anion channel-1 produced by a bacterial cell-free expression system. While VDAC structures have been recently solved, we propose an alternative strategy for producing the recombinant protein, which can be applied to other membrane proteins reluctant to expression, purification and crystallization by classical approaches. Despite a lot of efforts to crystallize a cell-free expressed membrane protein, this study is to our knowledge one of the first reports of a successful crystallization. Focusing on expression in a soluble and functional state, in a detergent environment, is the key to get crystals. Although the diffraction of VDAC crystals is limited, the simplicity and the rapidity to set-up and optimize this technology are drastic advantages in comparison to other methods

Phosphorylation of the Cav3.2 T-type calcium channel directly regulates its gating properties

Phosphorylation is a major mechanism regulating the activity of ion channels that remains poorly understood with respect to T-type calcium channels (Cav3). These channels are low voltage-activated calcium channels that play a key role in cellular excitability and various physiological functions. Their dysfunction has been linked to several neurological disorders, including absence epilepsy and neuropathic pain. Recent studies have revealed that T-type channels are modulated by a variety of serine/threonine protein kinase pathways, which indicates the need for a systematic analysis of T-type channel phosphorylation. Here, we immunopurified Cav3.2 channels from rat brain, and we used high-resolution MS to construct the first, to our knowledge, in vivo phosphorylation map of a voltage-gated calcium channel in a mammalian brain. We identified as many as 34 phosphorylation sites, and we show that the vast majority of these sites are also phosphorylated on the human Cav3.2 expressed in HEK293T cells. In patch-clamp studies, treatment of the channel with alkaline phosphatase as well as analysis of dephosphomimetic mutants revealed that phosphorylation regulates important functional properties of Cav3.2 channels, including voltage-dependent activation and inactivation and kinetics. We also identified that the phosphorylation of a locus situated in the loop I-II S442/S445/T446 is crucial for this regulation. Our data show that Cav3.2 channels are highly phosphorylated in the mammalian brain and establish phosphorylation as an important mechanism involved in the dynamic regulation of Cav3.2 channel gating properties

A novel phospho-modulatory mechanism contributes to the calcium-dependent regulation of T-type Ca2+ channels

International audienceca v 3 / T-type Ca 2+ channels are dynamically regulated by intracellular ca 2+ ions, which inhibit Ca v 3 availability. Here, we demonstrate that this inhibition becomes irreversible in the presence of non-hydrolysable ATP analogs, resulting in a strong hyperpolarizing shift in the steady-state inactivation of the residual ca v 3 current. Importantly, the effect of these ATP analogs was prevented in the presence of intracellular BAPTA. Additional findings obtained using intracellular dialysis of inorganic phosphate and alkaline phosphatase or nan 3 treatment further support the involvement of a phosphorylation mechanism. Contrasting with Ca v 1 and Ca v 2 Ca 2+ channels, the Ca 2+-dependent modulation of ca v 3 channels appears to be independent of calmodulin, calcineurin and endocytic pathways. Similar findings were obtained for the native T-type Ca 2+ current recorded in rat thalamic neurons of the central medial nucleus. Overall, our data reveal a new Ca 2+ sensitive phosphorylation-dependent mechanism regulating ca v 3 channels, with potentially important physiological implications for the multiple cell functions controlled by t-type ca 2+ channels

A simple method for the reconstitution of membrane proteins into giant unilamellar vesicles.

International audienceA simple method for the reconstitution of membrane protein from submicron proteoliposomes into giant unilamellar vesicles (GUVs) is presented here: This method does not require detergents, fusion peptides or a dehydration step of the membrane protein solution. In a first step, GUVs of lipids were formed by electroformation, purified and concentrated; and in a second step, the concentrated GUV solution was added to a small volume of vesicles or proteoliposomes. Material transfer from submicron vesicles and proteoliposomes to GUVs occurred spontaneously and was characterized with fluorescent microscopy and patch-clamp recordings. As a functional test, the voltage-dependent, anion-selective channel protein was reconstituted into GUVs, and its electrophysiological activity was monitored with the patch clamp. This method is versatile since it is independent of the presence of the protein, as demonstrated by the fusion of fluorescently labeled submicron vesicles and proteoliposomes with GUVs

An iPSC model of hereditary sensory neuropathy-1 reveals L-serine-responsive deficits in neuronal ganglioside composition and axoglial interactions

Hereditary sensory neuropathy type 1 (HSN1) is caused by mutations in the SPTLC1 or SPTLC2 sub-units of the enzyme serine palmitoyltransferase, resulting in the production of toxic 1-deoxysphingolipid bases (DSBs). We used induced pluripotent stem cells (iPSCs) from patients with HSN1 to determine whether endogenous DSBs are neurotoxic, patho-mechanisms of toxicity and response to therapy. HSN1 iPSC-derived sensory neurons (iPSCdSNs) endogenously produce neurotoxic DSBs. Complex gangliosides, which are essential for membrane micro-domains and signaling, are reduced, and neurotrophin signaling is impaired, resulting in reduced neurite outgrowth. In HSN1 myelinating cocultures, we find a major disruption of nodal complex proteins after 8 weeks, which leads to complete myelin breakdown after 6 months. HSN1 iPSC models have, therefore, revealed that SPTLC1 mutation alters lipid metabolism, impairs the formation of complex gangliosides, and reduces axon and myelin stability. Many of these changes are prevented by l-serine supplementation, supporting its use as a rational therapy