However, in future the full vista of S-prenylation could be opened up through a combination of improved prenyl analogues and quantitative gel-free metabolic labeling technologies previously successfully applied to N-myristoylation and S-acylation [ 12••, 13••, 25 and 26••]. Glycosylphosphatidylinositol (GPI)-anchored proteins are an abundant class of glycolipid-bearing Alectinib cell surface

proteins that provide one of the most important cellular machineries for extracellular communication in higher eukaryotes. GPI-anchored proteins are also implicated in many diseases including cancers, prion diseases and several parasitic infections [56, 57 and 58]. Although bioinformatics methods (e.g. PredGPI) can suggest potential GPI targets [59], experimental approaches for selective and quantitative profiling of modified proteins at a proteome-wide scale are limited. A recent study provides the first reported example of PTM-directed enrichment of GPI-anchored proteins through metabolic chemical tagging of the GPI lipid anchor [12••]. Exploiting the promiscuity of cellular fatty acid processing machineries, incubation of YnMyr with the malaria parasite P. falciparum led to metabolic labeling of NMT substrates (see above) and also GPI-anchored

Torin 1 concentration proteins, the latter including key mediators Erastin of immunogenicity and potential vaccine targets. A simple base-treatment prior to affinity enrichment

was sufficient to distinguish amide-linked N-myristoylation from ester-linked GPI O-myristoylation, and led to the identification of all known and several novel GPI-anchored proteins. This approach should prove applicable to global GPI protein profiling in other (e.g. human) systems. Protein cholesterylation has so far been observed only in the hedgehog (Hh) family of secreted proteins, which undergo posttranslational autocleavage of their C-terminal domain with concomitant O-cholesterylation at the C-terminal acid. Hh proteins are key players in embryonic development, stem cell maintenance and tissue repair, and as noted above are aberrantly overexpressed in several cancers [ 15]. Although the effects of loss of cholesterylation are readily modeled by deletion mutants, many questions concerning the role of intact wild-type cholesterylation remain unanswered due to the lack of robust tools to study the modification in living cells and in live organisms. The first report of chemical tagging of cholesterylation focused on the most studied member of the human Hh family, sonic hedgehog (Shh), and used an azide-tagged cholesterol analogue in a cell line [ 60]; whilst labeling was demonstrated, low efficiency and toxicity limited the scope of questions that could be addressed.