Proteomic analysis of palmitoylated platelet proteins.

Protein palmitoylation is a dynamic process that regulates membrane targeting of proteins and protein-protein interactions. We have previously demonstrated a critical role for protein palmitoylation in platelet activation and have identified palmitoylation machinery in platelets. Using a novel proteomic approach, Palmitoyl Protein Identification and Site Characterization, we have begun to characterize the human platelet palmitoylome. Palmitoylated proteins were enriched from membranes isolated from resting platelets using acyl-biotinyl exchange chemistry, followed by identification using liquid chromatography-tandem mass spectrometry. This global analysis identified > 1300 proteins, of which 215 met criteria for significance and represent the platelet palmitoylome. This collection includes 51 known palmitoylated proteins, 61 putative palmitoylated proteins identified in other palmitoylation-specific proteomic studies, and 103 new putative palmitoylated proteins. Of these candidates, we chose to validate the palmitoylation of triggering receptors expressed on myeloid cell (TREM)-like transcript-1 (TLT-1) as its expression is restricted to platelets and megakaryocytes. We determined that TLT-1 is a palmitoylated protein using metabolic labeling with [³H]palmitate and identified the site of TLT-1 palmitoylation as cysteine 196. The discovery of new platelet palmitoyl protein candidates will provide a resource for subsequent investigations to validate the palmitoylation of these proteins and to determine the role palmitoylation plays in their function.