J. Biochem, 2003, Vol. 133, No. 1 75-81
© 2003 Japanese Biochemical Society
BIOCHEMISTRY |
Crystal Structure of Hyperthermophilic Archaeal Initiation Factor 5A: A Homologue of Eukaryotic Initiation Factor 5A (eIF-5A)
1 Division of Biological Science, Graduate School of Science, Hokkaido University, Sapporo 066-0810; and 2 Laboratory of Biochemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University, Fukuoka 812-8581
Eukaryotic initiation factor 5A (eIF-5A) is ubiquitous in eukaryotes and archaebacteria and is essential for cell proliferation and survival. The crystal structure of the eIF-5A homologue (PhoIF-5A) from a hyperthermophilic archaebacterium Pyrococcus horikoshii OT3 was determined at 2.0 Å resolution by the molecular replacement method. PhoIF-5A is predominantly composed of ß-strands comprising two distinct folding domains, an N-domain (residues 169) and a C-domain (residues 72138), connected by a short linker peptide (residues 7071). The N-domain has an SH3-like barrel, while the C-domain folds in an (oligonucleotide/oligosaccharide binding) OB fold. Comparison of the structure of PhoIF-5A with those of archaeal homologues from Methanococcus jannaschii and Pyrobaculum aerophilum showed that the N-domains could be superimposed with root mean square deviation (rmsd) values of 0.679 and 0.624 Å, while the C-domains gave higher values of 1.824 and 1.329 Å, respectively. Several lines of evidence suggest that eIF-5A functions as a biomodular protein capable of interacting with protein and nucleic acid. The surface representation of electrostatic potential shows that PhoIF-5A has a concave surface with positively charged residues between the N- and C-domains. In addition, a flexible long hairpin loop, L1 (residues 3341), with a hypusine modification site is positively charged, protruding from the N-domain. In contrast, the opposite side of the concave surface at the C-domain is mostly negatively charged. These findings led to the speculation that the concave surface and loop L1 at the N-domain may be involved in RNA binding, while the opposite side of the concave surface in the C-domain may be involved in protein interaction.
+ To whom correspondence should be addressed. Tel/Fax: +81-92-642-2853, E-mail: mkimura{at}agr.kyushu-u.ac.jp
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