Final Report Summary - PALMERA (Roles of Palmitoylation networks in ER architecture and functions)
The workhorses of cells are proteins. Their function is controlled in time and in space. These regulatory mechanisms generally involve the post-translation modification of proteins by enzymatic reactions that add chemical moieties with specific properties. Some of these modifications are reversible, in the sense that cells express enzymes that add the chemical moiety in a regulated fashion but also express enzymes that remove it, in an equally controlled manner. One of these modifications is S-palmitoylation. It consists in the addition of a hydrocarbon chain, palmitate, to cysteine residues on the cytosolic side of proteins, modifying there hydrophobic properties. Addition of palmitate is performed by enzyme of the ZDHHC family, and removal occurs through the action of Acyl Protein Thioesterases or APTs. Despite the fact that some 2’000 proteins of the human proteome undergo this modification, very little is still known about the regulation, dynamics and consequences of this modification.
The human proteome has 23 ZDHHC enzymes and a yet unknown number of APTs. ZDHHC enzymes are membrane proteins and thus localize to membrane bound organelles in the cells. Half or more are found in the endoplasmic reticulum (ER), the first station of the secretory pathway and an organelle that is increasingly considered as a master regulator organelle that communicates with all others via physical contact sites.
The overall aim of this project was to increase our understanding of the dynamics and regulation of palmitoylation, with a particular focus on the endoplasmic reticulum. Two aspects were studied: 1) how palmitoylation-depalmitoylation cycles work, what is their “logics”? 2) what does palmitoylation do to proteins? In what way does it affect their function?
Interestingly we found that the palmitoylation system is highly interconnected. More specifically we found that palmitoyltransferases, as well as APTs are themselves palmitoylated. So, there are palmitoylation cascades, where one enzyme is activated by an upstream enzyme, while itself controlling down streams palmitoyltransferases. But ZDHHC enzymes also control the function of APTs, which affect them in return. This emerging complexity opens a vast domain of new research. We have also found that these palmitoylation events can be extremely dynamic, in some instances, while slow in others, again requiring further investigation.
We have furthermore actively investigated the consequence of palmitoylation using some model proteins. Some of the key observations include:
1) palmitoylation has a major influence on the architecture of the endoplasmic reticulum, affecting the interconversion of membrane tubules into flat structures, termed sheets;
2) palmitoylation plays a major role in the biogenesis of membrane proteins ensuring that cells express adequate amounts of transmembrane proteins;
3) Palmitoylation has major impact on protein turnover rates, leading to drastic decrease or increase depending on the protein;
4) finally palmitoylation can have major impact on protein localization and function and thereby constitutes interesting drug targets.
The human proteome has 23 ZDHHC enzymes and a yet unknown number of APTs. ZDHHC enzymes are membrane proteins and thus localize to membrane bound organelles in the cells. Half or more are found in the endoplasmic reticulum (ER), the first station of the secretory pathway and an organelle that is increasingly considered as a master regulator organelle that communicates with all others via physical contact sites.
The overall aim of this project was to increase our understanding of the dynamics and regulation of palmitoylation, with a particular focus on the endoplasmic reticulum. Two aspects were studied: 1) how palmitoylation-depalmitoylation cycles work, what is their “logics”? 2) what does palmitoylation do to proteins? In what way does it affect their function?
Interestingly we found that the palmitoylation system is highly interconnected. More specifically we found that palmitoyltransferases, as well as APTs are themselves palmitoylated. So, there are palmitoylation cascades, where one enzyme is activated by an upstream enzyme, while itself controlling down streams palmitoyltransferases. But ZDHHC enzymes also control the function of APTs, which affect them in return. This emerging complexity opens a vast domain of new research. We have also found that these palmitoylation events can be extremely dynamic, in some instances, while slow in others, again requiring further investigation.
We have furthermore actively investigated the consequence of palmitoylation using some model proteins. Some of the key observations include:
1) palmitoylation has a major influence on the architecture of the endoplasmic reticulum, affecting the interconversion of membrane tubules into flat structures, termed sheets;
2) palmitoylation plays a major role in the biogenesis of membrane proteins ensuring that cells express adequate amounts of transmembrane proteins;
3) Palmitoylation has major impact on protein turnover rates, leading to drastic decrease or increase depending on the protein;
4) finally palmitoylation can have major impact on protein localization and function and thereby constitutes interesting drug targets.