Activation segment dimerization: a mechanism for kinase autophosphorylation of non-consensus sites This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits distribution, and reproduction in any medium, provided the original author and source are credited. This license does not permit commercial exploitation or the creation of derivative works without specific permission

Protein kinase autophosphorylation of activation segment residues is a common regulatory mechanism in phospho- rylation-dependent signalling cascades. However, the mo- lecular mechanisms that guarantee specific and efficient phosphorylation of these sites have not been elucidated. Here, we report on three novel and diverse protein kinase structures that reveal an exchanged activation segment conformation. This dimeric arrangement results in an active kinase conformation in trans, with activation seg- ment phosphorylation sites in close proximity to the active site of the interacting protomer. Analytical ultracentrifu- gation and chemical cross-linking confirmed the presence of dimers in solution. Consensus substrate sequences for each kinase showed that the identified activation segment autophosphorylation sites are non-consensus substrate sites. Based on the presented structural and functional data, a model for specific activation segment phosphoryla- tion at non-consensus substrate sites is proposed that is likely to be common to other kinases from diverse subfamilies.