Abstract
SummarySki7 is a cofactor of the cytoplasmic exosome in budding yeast, functioning in both mRNA turnover and non-stop decay (NSD), a surveillance pathway that degrades faulty mRNAs lacking a stop codon. The C-terminal region of Ski7 (Ski7C) shares overall sequence similarity with the translational GTPase (trGTPase) Hbs1, but whether Ski7 has retained the properties of a trGTPase is unclear. Here, we report the high-resolution structures of Ski7C bound to either intact guanosine triphosphate (GTP) or guanosine diphosphate-Pi. The individual domains of Ski7C adopt the conformation characteristic of active trGTPases. Furthermore, the nucleotide-binding site of Ski7C shares similar features compared with active trGTPases, notably the presence of a characteristic monovalent cation. However, a suboptimal polar residue at the putative catalytic site and an unusual polar residue that interacts with the γ-phosphate of GTP distinguish Ski7 from other trGTPases, suggesting it might function rather as a GTP-binding protein than as a GTP-hydrolyzing enzyme.
Highlights
The decay of cytoplasmic mRNAs regulates the output of eukaryotic gene expression in terms of both quantity and quality
A suboptimal polar residue at the putative catalytic site and an unusual polar residue that interacts with the g-phosphate of guanosine triphosphate (GTP) distinguish Ski7 from other trGTPases, suggesting it might function rather as a GTP-binding protein than as a GTP-hydrolyzing enzyme
Structure Determination of the C-Terminal GTPase-Like Region of Ski7 We engineered a C-terminal fragment of S. cerevisiae Ski7 that encompasses the predicted GTPase-like region
Summary
Kowalinski et al report the crystal structure of the GTPase-like domain of yeast Ski, a protein module involved in non-stop decay, a ribosome-dependent mRNA surveillance pathway. This study shows that Ski interacts stably with guanosine triphosphate (GTP) and adopts the overall structural features of ribosome-associated GTPases. Highlights d The Ski C-terminal region adopts the conformation of active translational GTPases.
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