The intracellular dynamic of protein palmitoylation

Salaun, Christine; Greaves, Jennifer; Chamberlain, Luke H.

If the Golgi really is a super-reaction center for palmitoylation of peripheral proteins in mammalian cells, it will be of great interest to determine how this is achieved. Are Golgilocalized enzymes highly efficient? Are cofactors required for palmitoylation enriched at the Golgi? Do peripheral proteins interact in a slightly different way with Golgi membranes, making them more susceptible to palmitoylation? Most peripheral palmitoylated proteins associate with post-Golgi membranes (particularly the plasma membrane) after palmitoylation. Thus, specific palmitoylation at the Golgi might be an important prerequisite to ensure plasma membrane trafficking. A particular feature of palmitate that might facilitate Golgi to plasma membrane trafficking is its affinity for cholesterol-rich lipid raft domains (Melkonian et al., 1999; Levental et al., 2010) . It was recently proposed that raft domains might act as platforms for vesicle budding from the Golgi , and thus, palmitoylation-dependent association with these domains would be predicted to promote protein traffic to the plasma membrane. In support of the idea that palmitoylation at the Golgi is important for correct trafficking of peripheral proteins, we recently identified a connection between the palmitoylation of cysteine-string protein (CSP) at the Golgi and its subsequent sorting . A mutant form of CSP with an enhanced membrane affinity associates with ER membranes and is only palmitoylated when ER and Golgi membranes are mixed by applying brefeldin A . Interestingly, however, after washout of brefeldin A, the Golgi recovers but the CSP mutant remains trapped at the ER , perhaps reflecting a disconnect between forward transport of peripheral palmitoylated proteins and the lipid environment of ER membranes (cholesterol poor).