Crystal structure of YjeQ from Thermotoga maritima contains a circularly permuted GTPase domain

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Abstract
We have determined the crystal structure of the GDP complex of the YjeQ protein from Thermotoga maritima ( Tm YjeQ), a member of the YjeQ GTPase subfamaily. Tm YjeQ, a homologue of Escherichia coli YjeQ, which is known to bind to the ribosome, is composed of three domains: an N-terminal oligonucleotide/oligosaccharide-binding fold domain, a central GTPase domain, and a C-terminal zinc-finger domain. The crystal structure of Tm YjeQ reveals two interesting domains: a circularly permutated GTPase domain and an unusual zinc-finger domain. The binding mode of GDP in the GTPase domain of Tm YjeQ is similar to those of GDP or GTP analogs in ras proteins, a prototype GTPase. The N-terminal oligonucleotide/oligosaccharide-binding fold domain, together with the GTPase domain, forms the extended RNA-binding site. The C-terminal domain has an unusual zinc-finger motif composed of Cys-250, Cys-255, Cys-263, and His-257, with a remote structural similarity to a portion of a DNA-repair protein, rad51 fragment. The overall structural features of Tm YjeQ make it a good candidate for an RNA-binding protein, which is consistent with the biochemical data of the YjeQ subfamily in binding to the ribosome.