Abstract of the PDB Structure's related Publication:
H/ACA RNA-protein complexes, comprised of four proteins and an H/ACA guide RNA, modify ribosomal and small nuclear RNAs. The H/ACA proteins are also essential components of telomerase in mammals. Cbf5 is the H/ACA protein that catalyzes isomerization of uridine to pseudouridine in target RNAs. Mutations in human Cbf5 (dyskerin) lead to dyskeratosis congenita. Here, we describe the 2.1 A crystal structure of a specific complex of three archaeal H/ACA proteins, Cbf5, Nop10, and Gar1. Cbf5 displays structural properties that are unique among known pseudouridine synthases and are consistent with its distinct function in RNA-guided pseudouridylation. We also describe the previously unknown structures of both Nop10 and Gar1 and the structural basis for their essential roles in pseudouridylation. By using information from related structures, we have modeled the entire ribonucleoprotein complex including both guide and substrate RNAs. We have also identified a dyskeratosis congenita mutation cluster site within a modeled dyskerin structure.
Archaeal Cbf5 is the catalytic subunit of H/ACA small nucleolar ribonucleoprotein (H/ACA box snoRNP) complex. It catalyzes the pseudouridylation of rRNA, snRNA and also intron-containing pre-tRNA. It works with 3 other subunits, Gar1, Nop10 (two homologs of eukaryotic Gar1p/Nop10p), and ribosomal protein L7Ae that is unique to Archaea. However, only Nop10 seems important for tRNA modification. Archaeal L7Ae is the only core protein that is also shared by the C/D box snoRNP. Comparison of archaeal Cbf5 with bacterial tRNA Psi55 synthase (TruB) reveals structural conservation and provides insight into the guide-independent activity of archaeal Cbf5.