The third structural switch in the archaeal translation initiation factor 2 aIF2 molecule and its possible role in the initiation of GTP hydrolysis and the removal of aIF2 from the ribosome

Abstract

The structure of the amp; 947; subunit of archaeal translation initiation factor 2 aIF2 from Sulfolobus solfataricus SsoIF2 amp; 947; was determined in complex with GDPCP a GTP analog . Crystals were obtained in the absence of magnesium ions in the crystallization solution. They belonged to space group P1, with five molecules in the unit cell. Four of these molecules are related in pairs by a common non crystallographic twofold symmetry axis, while the fifth has no symmetry equivalent. Analysis of the structure and its comparison with other known aIF2 amp; 947; subunit structures in the GTP bound state show that i the magnesium ion is necessary for the formation and the maintenance of the active form of SsoIF2 amp; 947; and ii in addition to the two previously known structural switches 1 and 2, eukaryotic translation initiation factor 2 eIF2 and aIF2 molecules have another flexible region switch 3 , the function of which may consist of initiation of the hydrolysis of GTP and the removal of e aIF2 from the ribosome after codon anticodon recognitio