Mitogen-activated protein kinase kinase 5 (MAP2K5, alias MEK5) is a member of the ERK5 pathway, involved in angiogenesis and development [, ]. ERK5 is a MAPK activated in response to various stimuli through a three-tier cascade constituting MEK5 and MEKK2/3. MEK5 phosphorylates the activation loop of ERK5 at Thr218 and Tyr220 leading to its activation []. The PB1 domain of MEK5 interacts with the PB1 domains of other members of the kinase cascade, MEKK2 and MEKK3 [].The PB1s are dimerization/oligomerization domains present in adaptor and scaffold proteins as well as kinases and serve to organize platforms that ensure specificity and fidelity during cellular signalling []. The interaction between two PB1 domain depends on the type of PB1. There are three types of PB1 domains: type I which contains an OPCA motif, acidic aminoacid cluster, type II which contains a basic cluster, and type I/II which contains bothan OPCA motif and a basic cluster. The Map2k5 protein contains a type I PB1 domain [].
