Archaeal GPN-loop GTPases involve a lock-switch-rock mechanism for GTP hydrolysis

Abstract

ABSTRACT Three GPN-loop GTPases, GPN1–GPN3, are central to the maturation and trafficking of eukaryotic RNA polymerase II. This GTPase family is widely represented in archaea but typically occurs as single paralogs. Structural analysis of the GTP- and GDP-bound states of the Sulfolobus acidocaldarius GPN enzyme ( Sa GPN) showed that this central GPN-loop GTPase adopts two distinct quaternary structures. In the GTP-bound form, the γ-phosphate induces a closed dimeric arrangement by interacting with the GPN region that is relaxed upon hydrolysis to GDP. Consequently, a rocking-like motion of the two protomers causes a major allosteric structural change toward the roof-like helices. Using a lock-switch-rock mechanism, homo- and heterodimeric GPN-like GTPases are locked in the GTP-bound state and undergo large conformational changes upon GTP hydrolysis. A Δ saGPN strain of S. acidocaldarius was characterized by impaired motility and major changes in the proteome underscoring its functional relevance for S. acidocaldarius in vivo . IMPORTANCE GPN-loop GTPases have been found to be crucial for eukaryotic RNA polymerase II assembly and nuclear trafficking. Despite their ubiquitous occurrence in eukaryotes and archaea, the mechanism by which these GTPases mediate their function is unknown. Our study on an archaeal representative from Sulfolobus acidocaldarius showed that these dimeric GTPases undergo large-scale conformational changes upon GTP hydrolysis, which can be summarized as a lock-switch-rock mechanism. The observed requirement of Sa GPN for motility appears to be due to its large footprint on the archaeal proteome.