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I know that some kinases can phosporylate both serine and threonine residues because of their structural similarities, but can such a kinase phosphorylate a tyrosine residue as well?

If not, then why?

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Ony a few protein kinases can phosphorylate all three amino acids — these are classified as dual-specific kinases (EC 2.7.12.1). Examples are APK1 from Arabidopsis or MEK kinases in mammals.

As with other enzymes, the residues at the substrate binding site determine which substrates can be accomodated there. Structures or Ser- Thr- and Tyr-kinases are available for inspection, should you wish to explore them.

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  • $\begingroup$ Do you have a reference showing that the same catalytic domain in, for example, the MEK kinases phosphorylates both the Thr and Tyr simultaneously? I do know from working extensively with the MAPKs (Erk1/2 in particular) that the two residues can be under independent regulation. Part of that is obviously a function of different phosphatases, but I suspect there can be independent phosphorylation as well. Just not sure if it's by MEK1/2 or not. $\endgroup$
    – MattDMo
    Jun 1, 2016 at 12:08
  • $\begingroup$ Phosphorylation of MAP kinase by MEK at tyrosine 185 (pY185) and threonine 183 (pT183)...., ref: ncbi.nlm.nih.gov/books/NBK21529 $\endgroup$
    – Ashafix
    Jun 1, 2016 at 12:16
  • $\begingroup$ I have edited your original answer because, although essentially correct (+1), it had a mistakes in the EC number, and the Kegg link was specifically for MAPKs, whereas the Wiki page considers dual-specificity kinases, specifically. I also put in a link to the structures. As you had done the heavy lifting, I don't want to steal your thunder by posting an alternative answer. Do revert as you see fit. $\endgroup$
    – David
    Jun 1, 2016 at 12:23
  • $\begingroup$ Thanks for the edit! Can I give you half the credit? $\endgroup$
    – Ashafix
    Jun 1, 2016 at 12:26
  • $\begingroup$ @Ashafix yes, I'm aware of the "classical" understanding of the pathway, I'm talking about what really goes on in vivo. $\endgroup$
    – MattDMo
    Jun 1, 2016 at 12:38

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