Récepteur (biochimie) | EPFL Graph Search

En biochimie, un récepteur est une protéine de la membrane cellulaire ou du cytoplasme ou du noyau cellulaire qui se lie spécifiquement à un facteur spécifique (un ligand, tels un neurotransmetteur, une hormone, une molécule médicamenteuse, une toxine, un ion calcium, ou une protéine spécifique de la membrane d'un virus…), induisant une réponse cellulaire à ce ligand. Les modifications du comportement du récepteur protéique induites par le ligand conduisent à des modifications physiologiques qui constituent les « effets biologiques » du ligand. Comme toutes les protéines, les récepteurs ont leur structure primaire codée par un gène sur l'ADN. La plupart des gènes codant des hormones comportent une petite séquence qui indique à la cellule si elles doivent être transportées vers la membrane cellulaire ou si elles doivent rester dans le cytoplasme. Généralités De nombreuses maladies génétiques sont dues à des anomalies au niveau des gènes codant ces récepteurs. Parfois,

Functional characterization of a human odorant receptor

Valérie Jacquier

Olfaction appears to be mediated by a large family of odorant receptors (ORs) that accounts for ~ 1% of the human genome [1–4]. The functional characterization of these receptors has so far been hindered by their poor functional expression in the plasma membrane of heterologous cells. In order to investigate the problem of inefficient OR membrane targeting, sequential stages in the life cycle of the human OR17-40 were monitored. The modification of the receptor by different tags enabled the direct visualization of its biogenesis and trafficking in HEK293 cells. A multi-color labelling approach, which involved fluorescent subcellular markers as well as the spectral separation of membrane-inserted and intracellularly located receptors, indicated that high overexpression led to the accumulation of the receptor in the ER, whereas low expression levels improved its membrane targeting. To increase the efficiency of OR-mediated signalling, fluorescence-activated cell sorting of a functional OR17-40 – GFP fusion protein was used to separate low from high expressing cells, thus increasing the fraction of odorant-responsive cells up to 80% of the total cell population. Selectively labelled cell surface receptors accumulated over time in intracellular compartments, indicating constitutive receptor internalization. This process, which was independent of receptor activation, occurred along the clathrin-mediated pathway. Moreover, the imaging of single receptors in the plasma membrane indicated that, in absence of ligand, part of the receptors are already confined within small domains of 195 ± 10 nm. This fraction, which increased upon agonist or antagonist binding, probably corresponds to receptors located in clathrin-coated prepits. Odorant molecules structurally related to the cognate agonist helional were tested for their ability to activate OR17-40. It was found that an aldehyde group connected to an aromatic ring via a carbon chain of defined length and containing a methyl group in alpha or beta position is necessary for activating the receptor. In addition, first evidence for an OR17-40-specific antagonism was provided. Finally, OR17-40 activation was monitored in cell-derived native vesicles, opening new ways for assay miniaturization and the development of odorant screenings in a micro-array format.

EPFL2005

Single-Vesicle Assays Using Liposomes and Cell-Derived Vesicles: From Modeling Complex Membrane Processes to Synthetic Biology and Biomedical Applications

Horst Pick, Ana Catarina Rodrigues Alves, Horst Vogel

The plasma membrane is of central importance for defining the closed volume of cells in contradistinction to the extracellular environment. The plasma membrane not only serves as a boundary, but it also mediates the exchange of physical and chemical information between the cell and its environment in order to maintain intra- and intercellular functions. Artificial lipid- and cell-derived membrane vesicles have been used as closed-volume containers, representing the simplest cell model systems to study transmembrane processes and intracellular biochemistry. Classical examples are studies of membrane translocation processes in plasma membrane vesicles and proteoliposomes mediated by transport proteins and ion channels. Liposomes and native membrane vesicles are widely used as model membranes for investigating the binding and bilayer insertion of proteins, the structure and function of membrane proteins, the intramembrane composition and distribution of lipids and proteins, and the intermembrane interactions during exo- and endocytosis. In addition, natural cell-released microvesicles have gained importance for early detection of diseases and for their use as nanoreactors and minimal protocells. Yet, in most studies, ensembles of vesicles have been employed. More recently, new micro- and nanotechnological tools as well as novel developments in both optical and electron microscopy have allowed the isolation and investigation of individual (sub)micrometer-sized vesicles. Such single-vesicle experiments have revealed large heterogeneities in the structure and function of membrane components of single vesicles, which were hidden in ensemble studies. These results have opened enormous possibilities for bioanalysis and biotechnological applications involving unprecedented miniaturization at the nanometer and attoliter range. This review will cover important developments toward single-vesicle analysis and the central discoveries made in this exciting field of research.

AMER CHEMICAL SOC2018

HER receptor dimerization controlled with bivalent ligands

Seymour de Picciotto

In this thesis, I show the ability of engineered bivalent ligands to control HER signaling by taking advantage of the dimerization-dependent mechanism of the four different receptors in the HER (EGFR) family. While monovalent wild-type ligands form HER homoe- and hetero-dimers according to the different members' relative expression levels, I hypothesize that bivalent ligands are able to drive dimerization of specific family members, independently of the cell's HER receptor composition. Using human telomerase reverse transcriptase (hTERT)-immortalized human mesenchymal stem cells (hTMSC), this study first confirms the bioactivity of the bivalent ligands: they exhibit an EC50 one order of magnitude lower than wild-type monomeric ligands and shown an avidity effect as shown from dose-response analysis of the pERK and pY-EGFR nodes. Then, I take advantage of known differences between EGFR hetero- and homodimer to investigate the bivalent ligands' ability to form selective dimers. I demonstrate that bivalent EGF is capable of inducing greater EGFR phosphorylation while preventing HER2 phosphorylation compared to wild-type EGF stimulation. Furthermore, the kinetics of EGFR activation by bivalent EGF differs from wild-type EGF with the appearance of a second activation peak at 20 minutes. Controlling the HER signaling network with these bivalent ligands has potential applications in tissue engineering, cancer therapy and in fundamental studies of the ErbB receptors activation mechanism

2009