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12 páginas, 6 figuras. CSs fromTrkA-TMD and p75-TMD are deposited in the Biological Magnetic Resonance Data Bank with accession number 25872for TrkA-TMD and 19673 for p75-TMD., The neurotrophin receptors p75 and tyrosine protein kinase receptor A (TrkA) play important roles in the development and survival of the nervous system. Biochemical data suggest that p75 and TrkA reciprocally regulate the activities of each other. For instance, p75 is able to regulate the response of TrkA to lower concentrations of nerve growth factor (NGF), and TrkA promotes shedding of the extracellular domain of p75 by α-secretases in a ligand-dependent manner. The current model suggests that p75 and TrkA are regulated by means of a direct physical interaction; however, the nature of such interaction has been elusive thus far. Here, using NMR in micelles, multiscale molecular dynamics, FRET, and functional studies, we identified and characterized the direct interaction between TrkA and p75 through their respective transmembrane domains (TMDs). Molecular dynamics of p75-TMD mutants suggests that although the interaction between TrkA and p75 TMDs is maintained upon mutation, a specific protein interface is required to facilitate TrkA active homodimerization in the presence of NGF. The same mutations in the TMD protein interface of p75 reduced the activation of TrkA by NGF as well as reducing cell differentiation. In summary, we provide a structural model of the p75-TrkA receptor complex necessary for neuronal development stabilized by TMD interactions., This study was supported bythe Spanish Ministry of Economy and Competitiveness (project BFU2013-42746-P and SAF2017-84096-R), the GeneralitatValenciana Prometeo grant 2018/055 (to M. V.), and the National Institutes of Health GM068619 (to K. H.). NMR studies of TRKA-TM and p75-TM were supported by the Russian Science Founda-tion (grant no. 19-74-30014 to A. S. A.)

The neurotrophin receptors p75 and TrkA play an important role in the development and survival of the nervous system. Biochemical data suggest that p75 and TrkA regulate the activities of each other. For instance, p75 is able to regulate the response of TrkA to lower concentrations of NGF and TrkA promotes p75 shedding by α-secretases in a ligand-dependent manner. The current model is that p75 and TrkA are regulated by means of a physical direct interaction, however the nature of such interaction has been elusive so far. Here using NMR in micelles, multiscale molecular dynamics (MD), FRET and functional studies we identified and characterized the direct interaction between TrkA and p75 through the transmembrane domains (TMDs). MD of p75-TMD mutants suggests that although the interaction between TrkA and p75 TMDs is maintained, a specific protein interface is required to facilitate TrkA active homodimerization in the presence of NGF. The same mutations in the TMD protein interface of p75 reduced the activation of TrkA by NGF and cell differentiation. In summary we provide a structural model of the p75/TrkA receptor complex stabilized by transmembrane domain interactions.

20 páginas, 8 figuras, γ-secretase inhibitors (GSI) were developed to reduce the generation of Aβ peptide to find new Alzheimer's disease treatments. Clinical trials on Alzheimer's disease patients, however, showed several side effects that worsened the cognitive symptoms of the treated patients. The observed side effects were partially attributed to Notch signaling. However, the effect on other γ-secretase substrates, such as the p75 neurotrophin receptor (p75NTR) has not been studied in detail. p75NTR is highly expressed in the basal forebrain cholinergic neurons (BFCNs) during all life. Here, we show that GSI treatment induces the oligomerization of p75CTF leading to the cell death of BFCNs, and that this event is dependent on TrkA activity. The oligomerization of p75CTF requires an intact cholesterol recognition sequence (CRAC) and the constitutive binding of TRAF6, which activates the JNK and p38 pathways. Remarkably, TrkA rescues from cell death by a mechanism involving the endocytosis of p75CTF. These results suggest that the inhibition of γ-secretase activity in aged patients, where the expression of TrkA in the BFCNs is already reduced, could accelerate cholinergic dysfunction and promote neurodegeneration., This study was supported by the Spanish Minister of Economy and Competitiveness grant SAF2017-84096-R and by the Generalitat Valenciana 2018-55 to M Vilar. I García-Carpio was supported by an Formación de Personal Investigador (FPI) pre-doctoral fellowship (BFU2013/42746-P) and a mobility grant (EEBB-I-15-10278) from the Spanish Minister of Economy and Competitiveness. This work was funded by the Stichting Alzheimer Onderzoek (S16013) and the Fonds voor Wetenschappelijk Onderzoek or Flanders Research Foundation (FWO) research project (G0B2519N) to L Chavez-Gutiérrez

Artículo 10 páginas, 6 figuras. Contiene en material suplementario: Tabla S1 y Figs. S1–S7. This research was originally published in the Journal of Biological Chemistry. María L. Franco, Kirill D. Nadezhdin, Sergey A. Goncharuk, Konstantin S. Mineev, Alexander S. Arseniev, and Marçal Vilar. Structural basis of the transmembrane domain dimerization and rotation in the activation mechanism of the TRKA receptor by nerve growth factor. J. Biol. Chem. 2020; 295(1):275-286. © the American Society for Biochemistry and Molecular Biology., Tropomyosin-receptor kinases (TRKs) are essential for the development of the nervous system. The molecular mechanism of TRKA activation by its ligand nerve growth factor (NGF) is still unsolved. Recent results indicate that at endogenous levels most of TRKA is in a monomer-dimer equilibrium and that the binding of NGF induces an increase of the dimeric and oligomeric forms of this receptor. An unsolved issue is the role of the TRKA transmembrane domain (TMD) in the dimerization of TRKA and the structural details of the TMD in the active dimer receptor. Here, we found that the TRKA-TMD can form dimers, identified the structural determinants of the dimer interface in the active receptor, and validated this interface through site-directed mutagenesis together with functional and cell differentiation studies. Using in vivo cross-linking, we found that the extracellular juxtamembrane region is reordered after ligand binding. Replacement of some residues in the juxtamembrane region with cysteine resulted in ligand-independent active dimers and revealed the preferred dimer interface. Moreover, insertion of leucine residues into the TMD helix induced a ligand-independent TRKA activation, suggesting that a rotation of the TMD dimers underlies NGF-induced TRKA activation. Altogether, our findings indicate that the transmembrane and juxtamembrane regions of TRKA play key roles in its dimerization and activation by NGF., This work was supported by the Ministerio de Economía, Industria y Competitividad Projects BFU2013-42746-P and SAF2017-84096-R and by Generalitat Valenciana Prometeo Grant 2018/055 (to M. V.). The studies of TRKA-TM homodimerization were supported by Russian Science Foundation Grant 19-74-30014 (to A. S. A). The authors declare that they have no conflicts of interest with the contents of this article

13 páginas, 9 figuras. This research was originally published in Journal of Biological Chemistry. Franco M.L., Melero C., Sarasola E., Acebo P., Luque A., Calatayud-Baselga I., Garcia-Barcina M.,Vilar M. (2016). Mutations in TrkA causing congenital insensitivity to pain with anhidrosis (CIPA) induce misfolding, aggregation and mutation-dependent neurodegeneration by dysfunction of the autophagic flux. J Biol Chem 291(41): 21363-74. © the American Society for Biochemistry and Molecular Biology., Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder characterized by insensitivity to noxious stimuli and variable intellectual disability (ID) due to mutations in the NTRK1 gene encoding the NGF receptor TrkA. To get an insight in the effect of NTRK1 mutations in the cognitive phenotype we biochemically characterized three TrkA mutations identified in children diagnosed of CIPA with variable ID. These mutations are located in different domains of the protein; L213P in the extracellular domain, Δ736 in the kinase domain, and C300stop in the extracellular domain, a new mutation causing CIPA diagnosed in a Spanish teenager. We found that TrkA mutations induce misfolding, retention in the endoplasmic reticulum (ER), and aggregation in a mutation-dependent manner. The distinct mutations are degraded with a different kinetics by different ER quality control mechanisms; although C300stop is rapidly disposed by autophagy, Δ736 degradation is sensitive to the proteasome and to autophagy inhibitors, and L213P is a long-lived protein refractory to degradation. In addition L213P enhances the formation of autophagic vesicles triggering an increase in the autophagic flux with deleterious consequences. Mouse cortical neurons expressing L213P showed the accumulation of LC3-GFP positive puncta and dystrophic neurites. Our data suggest that TrkA misfolding and aggregation induced by some CIPA mutations disrupt the autophagy homeostasis causing neurodegeneration. We propose that distinct disease-causing mutations of TrkA generate different levels of cell toxicity, which may provide an explanation of the variable intellectual disability observed in CIPA patients., This work was supported in part by the Spanish Minister of Economy and Competitiveness Grants BFU2013/42746-P (to M. V.) and TPY-M-1068/13 (to A. L.). The authors declare that they have no conflicts of interest with the contents of this article.