Phosphoproteome analysis of the platelet plasma membrane.

Blood platelets are key players standing at the crossroads between physiologically occurring hemostasis and pathologic thrombus formation. As these cellular particles lack a nucleus, intra- and intercellular processes involved in platelet activity and function are almost exclusively regulated on the protein level. In particular, posttranslational protein modification by phosphorylation, which allows for a quick and highly dynamic transduction of cellular signals, is discussed in this context. In addition, since platelet activation and aggregation usually require surface contact with the surrounding tissue, special interest focuses on this contacting region, and hence on the subproteome of the platelet plasma membrane. In this chapter, we present a mass spectrometry-driven approach capable of dealing with the task of platelet plasma membrane proteomics and phosphoproteomics. The outlined protocols include strategies for the isolation and purification of plasma membrane proteins by aqueous two-phase partitioning and subsequent enrichment of phosphopeptides via titanium dioxide chromatography.