Insights into the Architecture of the eIF2Bα/β/δRegulatory Subcomplex

摘要

Eukaryotic translation initiation factor 2B (eIF2B), the guanine nucleotide exchange factor for the G-protein eIF2, is one of the main targets for the regulation of protein synthesis. The eIF2B activity is inhibited in response to a wide range of stress factors and diseases, including viral infections, hypoxia, nutrient starvation, and heme deficiency, collectively known as the integrated stress response. eIF2B has five subunits (α–ε). The α, β, and δ subunits are homologous to each other and form the eIF2B regulatory subcomplex, which is believed to be a trimer consisting of monomeric α, β, and δ subunits. Here we use a combination of biophysical methods, site-directed mutagenesis, and bioinformatics to show that the human eIF2Bα subunit is in fact a homodimer, at odds with the current trimeric model for the eIF2Bα/β/δ regulatory complex. eIF2Bα dimerizes using the same interface that is found in the homodimeric archaeal eIF2Bα/β/δ homologaIF2B and related metabolic enzymes. We also present evidence thatthe eIF2Bβ/δ binding interface is similar to that in theeIF2Bα2 homodimer. Mutations at the predicted eIF2Bβ/δdimer interface cause genetic neurological disorders in humans. Wepropose that the eIF2B regulatory subcomplex is an α2β2δ2 hexamer, composed of one α2 homodimer and two βδ heterodimers. Our resultsoffer novel insights into the architecture of eIF2B and its interactionswith the G-protein eIF2.