Exon Junction Complex
The exon junction complex (EJC) plays a major role in post-transcriptional regulation of mRNA in metazoa.
EJC is composed of four protein subunits, mRNA, and ATP. Four subunits are the following: elF4AIII (RNA helicase, yellow and red in Fig. 1), Barentsz (CASC3: cancer susceptibility candidate gene 3 protein, magenta), Mago (green), and Y14. (cyan)
The overall architecture is an L-shaped structure (Fig. 1). The two domains in elF4AIII form a cleft, which binds to the ATP molecule (Fig. 2).
RNA (blue in Fig. 1) binds to both of the two domains with a bent conformation. Barentsz does not take a globular fold but has an extended conformation. Shown in Fig. 1 is not the whole structure of Barentsz, but separated ones by experimental procedure. The interaction of Mago and Y14 is mediated by the α-helical surface of Mago and the β-sheet surface of the RNA binding domain of Y14. Both of these two proteins also interact with elF4AIII. Thus, the components of the EJC interact with each other and form an interaction network. The electrostatic interactions are involved in the network (Fig. 3). The network stabilizes the ATP binding mode in a cleft between the two domains in elF4AIII, anchoring Mago, Y14, and Barentsz with the interface of elF4AIII.
Protein Data Bank (PDB)
Bono, F. Ebert, J. Lorentzen, E. Conti, E.; "The crystal structure of the exon junction complex reveals how it maintains a stable grip on mRNA."; Cell(Cambridge,Mass.); (2006) 126:713-725 PubMed:16923391.
author: Daisuke Kuroda