Conformational transitions in the γ subunit of the archaeal translation initiation factor 2

In eukaryotes and archaea, the heterotrimeric translation initiation factor 2 (e/aIF2) is pivotal for the delivery of methionylated initiator tRNA (Met-tRNA_i) to the ribosome. It acts as a molecular switch that cycles between inactive (GDP-bound) and active (GTP-bound) states. Recent studies show that eIF2 can also exist in a long-lived eIF2γ–GDP–P_i (inorganic phosphate) active state. Here, four high-resolution crystal structures of aIF2γ from Sulfolobus solfataricus are reported: aIF2γ–GDPCP (a nonhydrolyzable GTP analogue), aIF2γ–GDP–formate (in which a formate ion possibly mimics P_i), aIF2γ–GDP and nucleotide-free aIF2γ. The structures describe the different states of aIF2γ and demonstrate the conformational transitions that take place in the aIF2γ `life cycle'.