Dual-Specificity Kinases

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Most protein kinases can phosphorylate on Serine or Threonine, and a distinct group (TKs) phosphorylates on tyrosine. Dual-specificty kinases are those than overall belong to Ser/Thr kinase groups, but can also phosphorylate on tyrosine. Several DSKs are well known, though many others may have tyrosine kinase activity at a low level or under specific circumstances. Here is a summary of the reported dual-specificity kinase classes.

Major classes of dual-specificty kinases


MEK kinases phosphorylate the activation loop of MAPK kinases, on both the T and Y of the TxY motif. Both phosphorylations are required for full activation of the MAPK. This motif is found in MAPKs throughout the eukaryotes, though some classes of MAPK lack the Y (e.g. Erk3, nmo) and are not activated by MEK kinases.


Wee1 phosphorylates CDK1/CDC2 on a tyrosine in the ATP-binding loop, and its metazoan paralog also phosphorylates the adjacent threonine (GxGTYG) [1]. Both phosphorylations are inhibitory, presumably by blocking ATP binding. Both T and Y are almost absolutely conserved throughout eukaryotic CDC2 genes.


Dyrk family kinases autophosphorylate on tyrosine, but transphosphorylate only on Ser/Thr (hence the name: "Dual specificity Tyrosine Regulated Kinase"). The autophosphorylation occurs while still attached to the ribosome, and is an intramolecular reaction [2]. Autophosphorylation occurs on a Y (YxY in DYRK1) in the activation loop which is almost absolutely conserved across all DYRK subfamilies. However, human Dyrk1A is active without this tyrosine phosphorylation, as shown in vitro in phosphatase-treated enzyme, or in mutants in which the substrate Ys are removed [3].


GSK3 is similar to DYRK in that an intramolecular autophosphorylation on an activation loop tyrosine occurs during maturation of the protein. In GSK3, the HSP90 chaperone is required to enable this phosphorylation [4]. After maturation, GSK3 is not seen to phosphorylate on tyrosine. GSK3 can be transphosphorylated by other tyrosine kinases, including MEK kinases in mammals and TKL kinases in Dictyostelium.

TKL group

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CK2 kinases have hundreds of substrates, including some tyrosine residues. Yeast CK2 phosphorylates FPR3 on Tyr184 (in vitro, and implied from a ts CK2 allele) [5]. Human CK2 has a similar activity in vitro, though tyrosine kinase activity is very weak when tested with peptide substrates. Mammalian CK2 is shown to autophosphorylate and to phosphorylate other substrates on tyrosine in vivo, with a specific substrate consensus motif found by peptide array profiling [6]. CK2 apparently autophosphorylates on Y182 and Y188 (on human CK2a1), which are within the activation loop and almost absolutely conserved in the CK2 family. Other substrates were inferred from pTyr staining of CK2-overexpressing cells but none were explicitly identified.

Questionable reports of dual-specificity kinases


The CLK family is related to DYRK, and members have been found to autophosphorylate and transphosphorylate on tyrosine in expression cloning in mammals, and in bacterial expression systems. However, in vivo substrates and physiological relevance of tyrosine phosphorylation is unclear. An activation loop tyrosine was seen to be phosphorylated in human CLK1 (http://www.phosphosite.org/proteinAction.do?id=2136&showAllSites=true), but this is only partially conserved (seen in CLK4 but is a F in CLK2/3 and also not conserved in invertebrates). At least one publication [7] suggests that the tyrosine kinase activity might be an artefact of kinase overexpression or in vitro assays. The Drosophila homolog, Doa, failed to phosphorylate the model tyrosine substrate polyGlu/Tyr in vitro [8]


Mouse Nek1 was isolated in an expression screen for tyrosine-phosphorylating proteins, and also shown to have tyrosine kinase activity in bacterial expression [9]. However, no native substrate for its tyrosine phosphorylation has been seen, and Nek2 has been shown not to phosphorylate on tyrosine [10].


The yeast homolog, rad53 (Spk1) was initially reported as being associated with dual specificity kinase activity [11], and another early report [12] showed weak tyrosine kinase activity in a fusion protein, induced tyrosine kinase activity in a bacterial transgene, and in vitro. However, the same report showed polyGlu/Tyr phosphorylation by CAMK2 and PKA, which are not otherwise known to have tyrosine kinase activity. There has been no further detailed analysis of this tyrosine kinase activity, and no known substrates have been found, casting some doubt on these early reports. Human Rad52 (Chk2) has been shown to be tyrosine phosphorylated on the activation loop, but the upstream kinase was not determined [13].


The Arabidopsis gene ADK1 (Arabidopsis Dual specificity Kinase 1) is a CK1 family member [14], isolated in an expression screen with anti-pTyr antibodies, and shown to tyrosine autophosphorylate and phosphorylate polyGluTyr. Bacterially-purified Xenopus CK1a was also shown to autophosphoryate weakly on tyrosine and to tyrosine phosphoryate two artificial substrates [15]. A focused study on human TDP-43 phosphorylation by CK1 showed a single tyrosine (Y4) to be phosphorylated by CK1 [16].


Bacterially-expressed Pim1 autophosphorylated weakly on tyrosine, in addition to strong Ser/Thr autophosphorylation [17]. Another report showed tyrosine-specific kinase activity, though in unusual conditions [18], but other studies showed only Ser and Thr autophosphorylation.


  1. Fattaey A and Booher RN. Myt1: a Wee1-type kinase that phosphorylates Cdc2 on residue Thr14. Prog Cell Cycle Res. 1997;3:233-40. PubMed ID:9552418 | HubMed [Fattaey]
  2. Lochhead PA, Sibbet G, Morrice N, and Cleghon V. Activation-loop autophosphorylation is mediated by a novel transitional intermediate form of DYRKs. Cell. 2005 Jun 17;121(6):925-36. DOI:10.1016/j.cell.2005.03.034 | PubMed ID:15960979 | HubMed [Lochhead1]
  3. Adayev T, Chen-Hwang MC, Murakami N, Lee E, Bolton DC, and Hwang YW. Dual-specificity tyrosine phosphorylation-regulated kinase 1A does not require tyrosine phosphorylation for activity in vitro. Biochemistry. 2007 Jun 26;46(25):7614-24. DOI:10.1021/bi700251n | PubMed ID:17536841 | HubMed [Adayev]
  4. Lochhead PA, Kinstrie R, Sibbet G, Rawjee T, Morrice N, and Cleghon V. A chaperone-dependent GSK3beta transitional intermediate mediates activation-loop autophosphorylation. Mol Cell. 2006 Nov 17;24(4):627-33. DOI:10.1016/j.molcel.2006.10.009 | PubMed ID:17188038 | HubMed [Lochhead2]
  5. Litchfield DW. Protein kinase CK2: structure, regulation and role in cellular decisions of life and death. Biochem J. 2003 Jan 1;369(Pt 1):1-15. DOI:10.1042/BJ20021469 | PubMed ID:12396231 | HubMed [Litchfield]
  6. Vilk G, Weber JE, Turowec JP, Duncan JS, Wu C, Derksen DR, Zien P, Sarno S, Donella-Deana A, Lajoie G, Pinna LA, Li SS, and Litchfield DW. Protein kinase CK2 catalyzes tyrosine phosphorylation in mammalian cells. Cell Signal. 2008 Nov;20(11):1942-51. DOI:10.1016/j.cellsig.2008.07.002 | PubMed ID:18662771 | HubMed [Vilk]
  7. Nayler O, Schnorrer F, Stamm S, and Ullrich A. The cellular localization of the murine serine/arginine-rich protein kinase CLK2 is regulated by serine 141 autophosphorylation. J Biol Chem. 1998 Dec 18;273(51):34341-8. PubMed ID:9852100 | HubMed [Nayler]
  8. Lee K, Du C, Horn M, and Rabinow L. Activity and autophosphorylation of LAMMER protein kinases. J Biol Chem. 1996 Nov 1;271(44):27299-303. PubMed ID:8910305 | HubMed [Lee]
  9. Letwin K, Mizzen L, Motro B, Ben-David Y, Bernstein A, and Pawson T. A mammalian dual specificity protein kinase, Nek1, is related to the NIMA cell cycle regulator and highly expressed in meiotic germ cells. EMBO J. 1992 Oct;11(10):3521-31. PubMed ID:1382974 | HubMed [Letwin]
  10. Fry AM, Schultz SJ, Bartek J, and Nigg EA. Substrate specificity and cell cycle regulation of the Nek2 protein kinase, a potential human homolog of the mitotic regulator NIMA of Aspergillus nidulans. J Biol Chem. 1995 May 26;270(21):12899-905. PubMed ID:7759549 | HubMed [Fry]
  11. Zheng P, Fay DS, Burton J, Xiao H, Pinkham JL, and Stern DF. SPK1 is an essential S-phase-specific gene of Saccharomyces cerevisiae that encodes a nuclear serine/threonine/tyrosine kinase. Mol Cell Biol. 1993 Sep;13(9):5829-42. PubMed ID:8355715 | HubMed [Zheng]
  12. Stern DF, Zheng P, Beidler DR, and Zerillo C. Spk1, a new kinase from Saccharomyces cerevisiae, phosphorylates proteins on serine, threonine, and tyrosine. Mol Cell Biol. 1991 Feb;11(2):987-1001. PubMed ID:1899289 | HubMed [Stern]
  13. Guo X, Ward MD, Tiedebohl JB, Oden YM, Nyalwidhe JO, and Semmes OJ. Interdependent phosphorylation within the kinase domain T-loop Regulates CHK2 activity. J Biol Chem. 2010 Oct 22;285(43):33348-57. DOI:10.1074/jbc.M110.149609 | PubMed ID:20713355 | HubMed [Guo]
  14. Ali N, Halfter U, and Chua NH. Cloning and biochemical characterization of a plant protein kinase that phosphorylates serine, threonine, and tyrosine. J Biol Chem. 1994 Dec 16;269(50):31626-9. PubMed ID:7527390 | HubMed [Ali]
  15. Pulgar V, Tapia C, Vignolo P, Santos J, Sunkel CE, Allende CC, and Allende JE. The recombinant alpha isoform of protein kinase CK1 from Xenopus laevis can phosphorylate tyrosine in synthetic substrates. Eur J Biochem. 1996 Dec 15;242(3):519-28. PubMed ID:9022677 | HubMed [Pulgar]
  16. Kametani F, Nonaka T, Suzuki T, Arai T, Dohmae N, Akiyama H, and Hasegawa M. Identification of casein kinase-1 phosphorylation sites on TDP-43. Biochem Biophys Res Commun. 2009 May 1;382(2):405-9. DOI:10.1016/j.bbrc.2009.03.038 | PubMed ID:19285963 | HubMed [Kametani]
  17. Palaty CK, Kalmar G, Tai G, Oh S, Amankawa L, Affolter M, Aebersold R, and Pelech SL. Identification of the autophosphorylation sites of the Xenopus laevis Pim-1 proto-oncogene-encoded protein kinase. J Biol Chem. 1997 Apr 18;272(16):10514-21. PubMed ID:9099695 | HubMed [Palatay]
  18. Telerman A, Amson R, Zakut-Houri R, and Givol D. Identification of the human pim-1 gene product as a 33-kilodalton cytoplasmic protein with tyrosine kinase activity. Mol Cell Biol. 1988 Apr;8(4):1498-503. PubMed ID:2837645 | HubMed [Telerman]
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