Protein kinase activation via autophosphorylation of a conserved threonine residue in their activation loop is a major regulatory mechanism shared by many kinases. In MAPKs, in addition to the conserved threonine residue, a neighboring tyrosine residue must also be phosphorylated for obtaining full catalytic activation. MAPK phosphorylation and activation is usually catalyzed by a relevant MAPK kinase. However, an increasing body of evidence supports the notion that MAPKs too can autophosphorylate and activate themselves, perhaps even on both the threonine and the tyrosine phospho-acceptors. MAPK autophosphorylation is not spontaneous, but rather regulated in vivo, suggesting that it is of biological relevance.
p38β is a unique MAPK in the sense that it manifests its autophosphorylation capability spontaneously as a recombinant purified protein. Recombinant purified p38β manifests its intrinsic activity not only towards itself, but also towards other substrates, probably as a result of this spontaneous autophosphorylation. Given the high sequence similarity between p38β and the other p38 isoforms, especially p38α, p38β is an excellent model to study the structure-function requirements for MAPK autophosphorylation.
Using a combination of experimental approaches, i.e testing the catalytic activity of recombinant purified proteins, expression in mammalian cell lines and yeast cells, we have managed to identify regions within p38β important for its intrinsic activity and began to study how this activity may be regulated in mammalian cells.