Aberg Espen, Torgersen Knut Martin, Johansen Bjarne, Keyse Stephen M, Perander Maria, Seternes Ole-Morten
Institutes of Pharmacy, Medical Biology, University of Tromsø, N-9037 Tromsø, Norway.
J Biol Chem. 2009 Jul 17;284(29):19392-401. doi: 10.1074/jbc.M109.023283. Epub 2009 May 27.
ERK3 and ERK4 are atypical MAPKs in which the canonical TXY motif within the activation loop of the classical MAPKs is replaced by SEG. Both ERK3 and ERK4 bind, translocate, and activate the MAPK-activated protein kinase (MK) 5. The classical MAPKs ERK1/2 and p38 interact with downstream MKs (RSK1-3 and MK2-3, respectively) through conserved clusters of acidic amino acids, which constitute the common docking (CD) domain. In contrast to the classical MAPKs, the interaction between ERK3/4 and MK5 is strictly dependent on phosphorylation of the SEG motif of these kinases. Here we report that the conserved CD domain is dispensable for the interaction of ERK3 and ERK4 with MK5. Using peptide overlay assays, we have defined a novel MK5 interaction motif (FRIEDE) within both ERK4 and ERK3 that is essential for binding to the C-terminal region of MK5. This motif is located within the L16 extension lying C-terminal to the CD domain in ERK3 and ERK4 and a single isoleucine to lysine substitution in FRIEDE totally abrogates binding, activation, and translocation of MK5 by both ERK3 and ERK4. These findings are the first to demonstrate binding of a physiological substrate via this region of the L16 loop in a MAPK. Furthermore, the link between activation loop phosphorylation and accessibility of the FRIEDE interaction motif suggests a switch mechanism for these atypical MAPKs in which the phosphorylation status of the activation loop regulates the ability of both ERK3 and ERK4 to bind to a downstream effector.
ERK3和ERK4是非典型丝裂原活化蛋白激酶（MAPK），经典MAPK激活环内的典型TXY基序被SEG取代。ERK3和ERK4都能结合、转位并激活MAPK激活的蛋白激酶（MK）5。经典MAPK ERK1/2和p38分别通过保守的酸性氨基酸簇与下游的MK（分别为RSK1 - 3和MK2 - 3）相互作用，这些酸性氨基酸簇构成了共同对接（CD）结构域。与经典MAPK不同，ERK3/4与MK5之间的相互作用严格依赖于这些激酶SEG基序的磷酸化。在此我们报告，保守的CD结构域对于ERK3和ERK4与MK5的相互作用并非必需。通过肽覆盖分析，我们在ERK4和ERK3中都确定了一个新的MK5相互作用基序（FRIEDE），它对于与MK5的C末端区域结合至关重要。该基序位于ERK3和ERK4中CD结构域C末端的L16延伸区内，并且FRIEDE基序中单个异亮氨酸到赖氨酸的取代完全消除了ERK3和ERK4对MK5的结合、激活和转位。这些发现首次证明了MAPK通过L16环的这一区域与生理底物的结合。此外，激活环磷酸化与FRIEDE相互作用基序可及性之间的联系表明了这些非典型MAPK的一种转换机制，其中激活环的磷酸化状态调节ERK3和ERK4与下游效应器结合的能力。
