Model-Driven Understanding of Palmitoylation Dynamics: Regulated Acylation of the Endoplasmic Reticulum Chaperone Calnexin

Tiziano Dallavilla, Laurence Gouzi Abrami, Vassily Hatzimanikatis, Patrick Alain Sandoz, Georgios Savoglidis, Françoise Gisou van der Goot Grunberg
Public Library of Science, 2016
Article

Résumé

Cellular functions are largely regulated by reversible post-translational modifications of proteins which act as switches. Amongst these, S-palmitoylation is unique in that it confers hydrophobicity. Due to technical difficulties, the understanding of this modification has lagged behind. To investigate principles underlying dynamics and regulation of palmitoylation, we have here studied a key cellular protein, the ER chaperone calnexin, which requires dual palmitoylation for function. Apprehending the complex inter-conversion between single-, double- and non- palmitoylated species required combining experimental determination of kinetic parameters with extensive mathematical modelling. We found that calnexin, due to the presence of two cooperative sites, becomes stably acylated, which not only confers function but also a remarkable increase in stability. Unexpectedly, stochastic simulations revealed that palmitoylation does not occur soon after synthesis, but many hours later. This prediction guided us to find that phosphorylation actively delays calnexin palmitoylation in resting cells. Altogether this study reveals that cells synthesize 5 times more calnexin than needed under resting condition, most of which is degraded. This unused pool can be mobilized by preventing phosphorylation or increasing the activity of the palmitoyltransferase DHHC6

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Tiziano Dallavilla, Laurence Gouzi Abrami, Vassily Hatzimanikatis, Patrick Alain Sandoz, Georgios Savoglidis, Françoise Gisou van der Goot Grunberg
Public Library of Science, 2016
Article

Résumé

Official source

https://infoscience.epfl.ch/record/217549?ln=fr

À propos de ce résultat

Concepts associés (13)

Concepts associés

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Publications associées (6)

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Communication and environment sensing are fundamental for the regulation of the majority of the cellular functions. In cells there are dedicated networks that are responsible for signalling, which gives the ability to the cell of sensing the external and internal environment allowing rapid response and adaptation to changes and stress events. A major component of these networks are post translational modifications. Their attachment to proteins in response to a change in the surrounding conditions can have very drastic consequences on modified proteins. Since post translational modification can heavily influence the cellular fate it is essential to identify these modifications and to understand their functioning, to better comprehend how cells respond to environments changes and different types of stress events to which they are continuously subjected. In this work we analyse a type of modification called S-palmitoylation, which is recently emerging as signalling/regulatory modification. S-Palmitoylation, or more generally âacylationâ, is the addition of an acyl chain to the SH-group of a cysteine via a thioester bond. This type of modification has a big impact at the cellular level. In different studies about palmitoylated proteins, functional consequences are observed at the cellular level, like altered signalling capacity, activity modulation, regulation of protein stability and localization. Palmitoylation was studied using a mathematical modelling approach. Based on experimental data we developed models of the palmitoylation process of different proteins. Using a bottom up approach we first investigated the consequences of protein palmitoylation on the endoplasmic reticulum chaperone calnexin, to better understand the consequences of palmitoylation at the protein level. Following the same approach we investigated the effects of palmitoylation on DHHC6, a palmitoyltransferase that is responsible for palmitoylation of calnexin, which itself undergoes palmitoylation from the palmitoyltransferase DHHC16. In the last part of the project we focused on the study of palmitoylation at the network level. For this purpose we reconstructed the palmitoylation cascade of calnexin, including in the model all the proteins involved in the palmitoylation process of this protein. This network of palmitoylation allowed us to investigate the dynamics of palmitoylation at the network level, focusing in the characterization of those mechanisms that are responsible for regulation of palmitoylation on different substrates. This work provides an unprecedented level of understanding of palmitoylation dynamics, both at the protein and network level. Moreover all the models and the tools for model analysis used in this work have been developed keeping in mind the final goal of reconstructing the entire palmitoylation network. Thanks to the approach we chose for modelling, the calnexin network model developed during this project can be easily expanded to include other portions of the palmitoylation networks. Similarly the tools developed for model analysis can be easily adapted to work on post-translational modification assays and analysis of biological functions from the smaller to the larger scales.

EPFL2017

Chargement

Palmitoylation of membrane proteins (Review)

Françoise Gisou van der Goot Grunberg

S-Palmitoylation is a reversible post-translational modification that results in the addition of a C16-carbon saturated fatty acyl chain to cytoplasmic cysteine residues. This modification is mediated by Palmitoyl-acyl Transferases that are starting to be investigated, and reversed by Protein Palmitoyl Thioesterases, which remain enigmatic. Palmitoylation of cytoplasmic proteins has been well described to regulate the interaction of these soluble proteins with specific membranes or membrane domains. Less is known about the consequences of palmitoylation in transmembrane proteins not only due to the dual difficulty of following a lipid modification and dealing with membrane proteins, but also due to the complexity of the palmitoylation-induced behavior. Moreover, possibly because the available data set is limited, the change in behavior induced by palmitoylation of a transmembrane protein is currently not predictable. We here review the various consequences reported for the palmitoylation of membrane proteins, which include improper folding in the endoplasmic reticulum, retention in the Golgi, inability to assemble into protein platforms, altered signaling capacity, premature endocytosis and missorting in the endocytic pathway. We then discuss the possible underlying mechanisms, in particular the ability of palmitoylation to control the conformation of transmembrane segments, to modify the affinity of a membrane protein for specific membrane domains and to control protein-protein interactions.

Taylor & Francis2008

Chargement

Palmitoylated calnexin is a key component of the ribosome-translocon complex

Sanja Blaskovic, Matteo Dal Peraro, Laurence Gouzi Abrami, Béatrice Kunz, Thomas Lemmin, Françoise Gisou van der Goot Grunberg

A third of the human genome encodes N-glycosylated proteins. These are co-translationally translocated into the lumen/membrane of the endoplasmic reticulum (ER) where they fold and assemble before they are transported to their final destination. Here, we show that calnexin, a major ER chaperone involved in glycoprotein folding is palmitoylated and that this modification is mediated by the ER palmitoyltransferase DHHC6. This modification leads to the preferential localization of calnexin to the perinuclear rough ER, at the expense of ER tubules. Moreover, palmitoylation mediates the association of calnexin with the ribosome-translocon complex (RTC) leading to the formation of a supercomplex that recruits the actin cytoskeleton, leading to further stabilization of the assembly. When formation of the calnexin-RTC supercomplex was affected by DHHC6 silencing, mutation of calnexin palmitoylation sites or actin depolymerization, folding of glycoproteins was impaired. Our findings thus show that calnexin is a stable component of the RTC in a manner that is exquisitely dependent on its palmitoylation status. This association is essential for the chaperone to capture its client proteins as they emerge from the translocon, acquire their N-linked glycans and initiate folding. The EMBO Journal (2012) 31, 1823-1835. doi: 10.1038/emboj.2012.15; Published online 7 February 2012

2012

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EPFL2017