ИСТИНА

The density regulated protein (DENR) and the malignant T cell-amplified sequence 1 (MCT-1/MCTS1) oncoprotein support noncanonical translation initiation, promote translation reinitiation on a specific set of mRNAs with short upstream reading frames and regulate ribosome recycling. DENR and MCT-1 form a heterodimer, which binds to the ribosome. We determined the crystal structures of the C-terminal domain of DENR and the heterodimer formed by human MCT-1 and the N-terminal domain of DENR at 1.74 Å and 2.0 Å resolution, respectively. The structure of the heterodimer reveals atomic details of the mechanism of DENR and MCT-1 interaction. Four conserved cysteine residues of DENR (C34, C37, C44, C53) form a classical tetrahedral zinc ion-binding site, which preserves the structure of the DENR’s MCT-1 binding interface that is essential for the dimerization. Substitution of all four cysteines by alanine abolished a heterodimer formation. The structure of the C-terminal domain of DENR has a striking similarity with those of canonical initiation factor 1 (eIF1), which controls the fidelity of translation initiation and scanning. In addition, the C-terminal domain of DENR was crystalized in three different conformations, which may reflect its physiological flexibility. The likelihood of this conformational flexibility was investigated by molecular dynamics simulation. Our findings elucidate further the mechanism of regulation of DENR-MCT-1 activities in unconventional translation initiation, reinitiation and recycling.