Background: Activation of mitogen-activated protein kinases (MAPKs) is regulated by
a phosphorylation cascade comprising three kinases, MAPK kinase kinase (MAP3K), MAPK kinase
(MAP2K), and MAPK. MAP2K1 and MAPK2K2, also known as MEK1 and MEK2, activate
ERK1 and ERK2. The structure of the MAPK signaling cascade has been studied, but high-resolution
structural studies of MAP2Ks have often focused on kinase domains or docking sites, but not
on full-length proteins.
Objective: To understand the conformational dynamics of MEK1.
Methods: Full-length MEK1 was purified from Escherichia coli (BL21), and its conformational dynamics
were analyzed using hydrogen/deuterium exchange mass spectrometry (HDX-MS). The effects
of ATP binding were examined by co-incubating MEK1 and adenylyl-imidodiphosphate (AMP-
PNP), a non-hydrolysable ATP analog.
Results: MEK1 exhibited mixed EX1/EX2 HDX kinetics within the N-terminal tail through β1, αI,
and the C-terminal helix. AMP-PNP binding was found to reduce conformational dynamics within
the glycine-rich loop and regions near the DFG motif, along with the activation lip.
Conclusion: We report for the first time that MEK1 has regions that slowly change its folded and
unfolded states (mixed EX1/EX2 kinetics) and also report the conformational effects of ATP-binding