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Protein phosphorlyation is the most widespread and studied regulatory signaling mechanism occurring in both eukaryotic and prokaryotic organisms. The mechanism of adding phosphate (PO4) to a protein by a kinase forms the basis of cell signaling networks involved in all fundamental cellular processes (1,2,3). However, the biochemical identification of the substrates for any kinase of interest (KOI) has been challenging and limited. This is due to the low abundance of most phosphoproteins, coupled with substoichiometric phosphorylation, and weak affinity of kinase-substrate interactions. Here we describe and illustrate the semi-synthetic kinase substrate tagging and detection technique using a novel thiophosphate ester specific monoclonal antibody first introduced by Allen et al. (5,6).
MethodsThe semi-synthetic epitope tagging reaction was carried out as in Figure 1. First a KOI (JNK1, 10 μ ng) was incubated with c-jun-GST substrate (1 g), with ATPγS as a thiophosphate donor. Thiophosphorylated c-jun-GST was then alkylated with p-nitrobenzyl mesylate (PNBM, 2.5 mM). The kinase reaction was carried out for 30 min at room temperature. Then PNBM alkylation (2.5 mM) proceeded for 2 h at room temperature. Reaction products were then analyzed by Western blot using the thiophosphate ester specific monoclonal antibody (clone 51-8; Epitomics, Inc. Burlingame, CA, USA) at 1:5000. Antibodies were incubated overnight at 4°C. α-GST antibody confirmed equal loading (Figure 2).
Conclusion
By utilizing the novel rabbit monoclonal antibody (clone 51-8) to detect proteins containing thiophosphate ester site following labeling, one can identify both known and novel substrates as well as detect context independent serine, threonine, and tyrosine phosphorylated substrates. This semi-synthetic epitope tagging provides a new way to identify and isolate substrates of various kinases (4,5,6). Visit www.epitomics.com/kinase to learn more.
ContactEpitomics, Inc. 863 Mitten Road, Suite 103, Burlingame, CA. info@epitomics.com, www.epitomics.com
