Modification post-traductionnelle

Une modification post-traductionnelle est une modification chimique d'une protéine, réalisée le plus souvent par une enzyme, après sa synthèse ou au cours de sa vie dans la cellule. Généralement cette modification entraîne un changement de la fonction de la protéine considérée, que ce soit au niveau de son action, de sa demi-vie, ou de sa localisation cellulaire. Addition d'un groupe fonctionnel

l'acétylation, soit l'addition d'un groupe acétyl provenant de l'acétyl-CoA, catalysé par un petit nombre d'enzyme (de type N-acétyl transférases), généralement au niveau de l'extrémité N-terminal d'une protéine ; néanmoins, cette modification qui intervient durant la synthèse de la proteine est essentiellement cotraductionelle bien que généralement considérée, à tort, comme une modification post-traductionelle ;
l'alkylation, soit l'addition d'un groupe alkyl, méthyl ou éthyl ; ** la méthylation est l'addition d'un groupe méthyl, généralement sur les acides aminés lysine ou arg

Crosstalk between Drp1 phosphorylation sites during mitochondrial dynamics and metabolic adaptation

Miriam Valera Alberni

Mitochondria are highly dynamics organelles that undergo coordinated cycles of fission and fusion, referred to as mitochondrial dynamics. Mitochondrial dynamics regulate mitochondrial bioenergetics and allow cells to adapt to changing cellular stresses and physiological challenges. The balance between different GTPase enzymes dictates the shift from interconnected tubular networks to fragmented individual units. Among them, mitochondrial fission is regulated by the mitochondrial fission orchestrator, Drp1. Drp1 function is modulated by post-translational modifications, of which the phosphorylation at two specific sites have gained most attention. Drp1 phosphorylation at the S579 site results in Drp1 recruitment to mitochondria to promote fission, whereas the research on the role of the Drp1 S600 phosphorylation have yielded contradictory results on whether it promotes fission or fusion. Importantly, the crosstalk and physiological impact of these phosphorylations is poorly understood. In this project, we focused first on elucidating the interplay between Drp1 S600 and Drp1 S579 phosphorylations. We described how Drp1 S600 phosphorylation promotes S579 phosphorylation by protecting against its dephosphorylation. The activation at both S600 and S579 sites is required to, then, promote mitochondrial fragmentation. To explore the physiological relevance of these phosphorylations, we generated a Drp1 S600A knock-in (Drp1KI) mouse model. Drp1KI mice displayed enhanced lipid oxidation rates and respiratory capacity, granting improved glucose tolerance and thermogenic capacity upon high-fat feeding. Housing mice at thermoneutrality blunted these differences, suggesting a role for the brown adipose tissue in the protection of Drp1KI mice against metabolic damage. Therefore, this work unveils for the first time the crosstalk between Drp1 phosphorylation sites and their relationship to impact on mitochondrial architecture. Moreover, we demonstrate that targeting the Drp1 S600 site can grant protection against diet-induced insulin resistance, suggesting that the modulation of these phosphorylations could be used in the treatment and prevention of metabolic diseases.

EPFL2020

Novel systems biology approaches for design and analysis of palmitoylation networks reveal its regulatory effects on protein stability, activity and localization

Tiziano Dallavilla

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

Crosstalk between Drp1 phosphorylation sites during mitochondrial dynamics and metabolic adaptation

Miriam Valera Alberni

EPFL2020

Novel systems biology approaches for design and analysis of palmitoylation networks reveal its regulatory effects on protein stability, activity and localization

Tiziano Dallavilla

EPFL2017