Structure-function relationships of the intact aIF2alpha subunit from the archaeon Pyrococcus abyssi

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Eukaryotic and archaeal initiation factor 2 (eIF2/aIF2) are essential heterotrimeric proteins (αβγ) for initiating protein synthesis.
• The alpha (α) subunit, in conjunction with the gamma (γ) subunit, dictates the tRNA binding capacity of the initiation factor.

Purpose of the Study:

• To determine the crystallographic structure of the intact archaeal aIF2α subunit from *Pyrococcus abyssi*.
• To compare the structural organization of archaeal aIF2α with its eukaryotic counterparts (yeast and human eIF2α).

Main Methods:

• X-ray crystallography was employed to obtain the structures of the intact aIF2α and a C-terminal fragment (domains 2 and 3).
• Comparative structural analysis was performed against existing crystal and NMR structures of human and yeast eIF2α.

Main Results:

• The three-domain organization of the aIF2α subunit is conserved across archaea and eukaryotes.
• Domains 1 and 2 form a rigid body, while domain 3 exhibits significant structural mobility.
• Highly conserved regions, implicated in RNA binding, are located in domains 1 and 3.

Conclusions:

• The conserved, yet mobile, structure of aIF2α suggests an integral role in ribosome and tRNA interactions.
• Domain 3 likely mediates binding to both the gamma subunit and methionyl-tRNA(i)(Met).
• Domain 1 is proposed to interact with ribosomal RNA or messenger RNA, facilitating accurate initiation complex formation.