Biology subjects

Franco, M. L.

Publications and source records attributed to Franco, M. L..

5 recordsLinked to original sources

bioRxiv2023

Alzheimer's disease linked Aβ42 exerts product feedback inhibition on γsecretase impairing downstream cell signaling

Amyloid {beta} (A{beta}) peptides accumulating in the brain are proposed to trigger Alzheimers disease (AD). However, molecular cascades underlying their toxicity are poorly defined. Here, we explored a novel hypothesis for A{beta}42 toxicity that arises from its proven affinity for {gamma}-secretases. We hypothesized that the reported increases in A{beta}42, particularly in the endolysosomal compartment, promote the establishment of a product feedback inhibitory mechanism on {gamma}-secretases, and thereby impair downstream signaling events. We show that human A{beta}42 peptides, but neither murine A{beta}42 nor human A{beta}17-42 (p3), inhibit {gamma}-secretases and trigger accumulation of unprocessed substrates in neurons, including C-terminal fragments (CTFs) of APP, p75 and pan-cadherin. Moreover, A{beta}42 treatment dysregulated cellular homeostasis, as shown by the induction of p75-dependent neuronal death in two distinct cellular systems. Our findings raise the possibility that pathological elevations in A{beta}42 contribute to cellular toxicity via the {gamma}-secretase inhibition, and provide a novel conceptual framework to address A{beta} toxicity in the context of {gamma}-secretase-dependent homeostatic signaling.

biochemistry↗

bioRxiv2023

Structural Basis for the transmembrane signaling and antidepressant-induced activation of the receptor tyrosine kinase TrkB

Neurotrophin receptors of the Trk family are involved in the regulation of brain development and neuroplasticity, and therefore can serve as targets for anti-cancer and stroke-recovery drugs, antidepressants, and many others. The structures of Trk protein domains in various states upon activation need to be elucidated to allow rational drug design. However, little is known about the conformations of the transmembrane and juxtamembrane domains of Trk receptors. In the present study, we employed NMR spectroscopy to solve the structure of the TrkB dimeric transmembrane domain in the lipid environment. We verified the structure using mutagenesis and confirmed that the conformation corresponds to the active state of the receptor. Subsequent study of TrkB interaction with the antidepressant drug fluoxetine, and the antipsychotic drug chlorpromazine, provided a clear self-consistent model, describing the mechanism by which fluoxetine activates the receptor by binding to its transmembrane domain.

biochemistry↗

bioRxiv2022

Identification of a guanine-specific pocket in the protein N of SARS-CoV-2

The SARS-CoV-2 nucleocapsid protein (N) is responsible for RNA binding. Here we report the crystal structure of the C-terminal domain (NCTD) in open and closed conformations and in complex with guanine triphosphate, GTP. The crystal structure and biochemical studies reveals a specific interaction between the guanine, a nucleotide enriched in the packaging signals regions of coronaviruses, and a highly conserved tryptophan residue (W330). In addition, EMSA assays with SARS-CoV-2 derived RNA hairpin loops from a putative viral packaging sequence showed the preference interaction of the N-CTD to RNA oligonucleotides containing G and the loss of the specificity in the mutant W330A. Here we propose that this interaction may facilitate the viral assembly process. In summary we have identified a specific guanine-binding pocket in the N protein that may be used to design viral assembly inhibitors.

biophysics↗

bioRxiv2021

Neurotrophin signaling is modulated by specific transmembrane domain interactions

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 -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.

biochemistry↗

bioRxiv2019

Structural Basis and Mechanism of TrkA Activation by NGF through Ligand-Induced Rotation of Transmembrane Domain Dimers.

Trk receptors are essential for the nervous system development. The molecular mechanism of TrkA activation by its ligand NGF is still unsolved. Recent data indicates that at endogenous levels most of TrkA is in an equilibrium monomer-dimer and the binding of NGF induces an increase of the dimer and oligomer forms of the receptor. An unsolved issue is the role of the transmembrane domain (TMD) in the dimerization of TrkA and the structural details of the TMD in the active dimer receptor. We found that TrkA-TMD can form dimers, identified the structural determinants of the dimer interface in the active receptor and validated this interface using site-directed mutagenesis together with functional and cell differentiation studies. Using in vivo crosslinking we identified a reordering of the extracellular juxtamembrane (JTM) region after ligand binding. Replacement of some residues in the JTM region with cysteine form ligand-independent active dimers and reveal a preferred dimer interface. In addition to that, insertion of leucine residues into the TMD helix induces a ligand-independent TrkA activation suggesting that a rotation of the TMD dimers could be behind TrkA activation by NGF. Altogether our data indicates that the transmembrane and juxtamembrane regions of the receptor play a key role in the dimerization and activation of TrkA by NGF.

biochemistry↗