Background
Ubiquitin (Ub) is a highly conserved 76 amino-acid protein found throughout eukaryotic cells. A vast number of cellular processes, including targeted protein degradation, cell cycle progression, DNA repair, protein trafficking, inflammatory response, virus budding, and receptor endocytosis, are regulated by Ub-mediated signalling; where the target protein is tagged by single or multi-monomeric Ub (monomeric Ub attached to multiple sites on the substrate) or a polymeric chain of Ubs (Fushman and Walker, 2010). More recently the demonstration that ubiquitin itself can be modified through phosphorylation by the kinase PTEN Induced putative Kinase1 (PINK1) provides a major breakthrough linking the two most important signalling pathways in cells; phosphorylation and ubiquitylation (Kane et al., 2014; Kazlauskaite et al., 2014; Koyano et al., 2014). Several studies have revealed that PINK1 directly phosphorylates ubiquitin on Ser65 a residue that is also shared by the Parkin Ubl domain (Kane et al., 2014; Kazlauskaite et al., 2014; Koyano et al., 2014). Parkin is activated by Ser65 phosphorylated ubiquitin in a manner which is independent of ubiquitin's ability to be conjugated. The mechanism of Parkin priming and activation is thought to occur through a conformational change induced by PINK1 phosphorylation on Ser65 followed by the binding of PINK1 Ser65 phosphorylated ubiquitin on the RING1 domain which optimises the ubiquityla tion activity of Parkin (Kazlauskaite et al., 2014; Koyano et al., 2014). Phospho-ubiquitin may play other roles in regulating Parkin but more generally the identification of phospho-ubiquitin as a second messenger in signalling pathways could reveal the existence of further ubiquitin phosphatases and lead to the discovery of additional kinase and ubiquitin related substrates (Sauve and Gehring, 2014).
Phosphoproteomic studies have identified the presence of several phosphorylated peptides demonstrating homology to proteins of the Ubiquitin Proteasome Pathway (UPP) these include ubiquitin (pSer57 being among those identified), ubiquitin like modifiers and proteins containing ubiquitin binding domains (Bennetzen et al., 2010; Bian et al., 2014; Moritz et al., 2010; Sharma et al., 2014).
Ubiquitin (pSer57) (Cat# 60-0208-050) is a phosphorylated synthetically made ubiquitin which may be used alongside Biotin-Ahx-Ubiquitin (pSer57) (Cat# 60-0205-050) and the non-phosphorylated control Ubiquitin (synthetic) (Cat# 60-0200-050).
References
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Bian Y, Song C, Cheng K, Dong M, Wang F, et al. (2014) An enzyme assisted RP-RPLC approach for in-depth analysis of human liver phosphoproteome. J Proteomics 16, 253-62.
Fushman D and Walker O (2010) Exploring the linkage dependence of polyubiquitin conformations using molecular modeling.Journal of Molecular Biology 395, 803-814.
Kane LA, Lazarou M, Fogel AI, Li Y, Yamano K, Sarraf SA, et al.(2014) PINK1 phosphorylates ubiquitin to activate Parkin E3 ubiquitin ligase activity. J Cell Biol 205, 143-153.
Kazlauskaite A, Kondapalli C, Gourlay R, Campbell DG, Ritorto MS, Hofmann K, et al.(2014) Parkin is activated by PINK1-dependent phosphorylation of ubiquitin at Ser65. Biochem J 460, 127-139.
Kettenbach AN, Schweppe DK, Faherty BK, Pechenick D, Pletnev AA and Gerber SA (2011) Quantitative phosphoproteomics identifies substrates and functional modules of Aurora and Pololike kinase activities in mitotic cells. Sci Signal 4, rs5.
Koyano F, Okatsu K, Kosako H, Tamura Y, Go E, Kimura M, et al.(2014) Ubiquitin is phosphorylated by PINK1 to activate parkin. Nature 510, 162-166.
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Sharma K, D'Souza RC, Tyanova S, Schaab C, Wisniewski JR, Cox J, et al.(2014) Ultradeep human phosphoproteome reveals a distinct regulatory nature of Tyr and Ser/Thr-based signaling. Cell Rep 8, 1583-1594.