Abstract
Rix7 is an essential type II AAA-ATPase required for the formation of the large ribosomal subunit. Rix7 has been proposed to utilize the power of ATP hydrolysis to drive the removal of assembly factors from pre-60S particles, but the mechanism of release is unknown. Rix7’s mammalian homolog, NVL2 has been linked to cancer and mental illness disorders, highlighting the need to understand the molecular mechanisms of this essential machine. Here we report the cryo-EM reconstruction of the tandem AAA domains of Rix7 which form an asymmetric stacked homohexameric ring. We trapped Rix7 with a polypeptide in the central channel, revealing Rix7’s role as a molecular unfoldase. The structure establishes that type II AAA-ATPases lacking the aromatic-hydrophobic motif within the first AAA domain can engage a substrate throughout the entire central channel. The structure also reveals that Rix7 contains unique post-α7 insertions within both AAA domains important for Rix7 function.
Highlights
Rix[7] is an essential type II AAA-ATPase required for the formation of the large ribosomal subunit
Their proposed function is to utilize the power of atoms Protein residues Ligands (ATP) hydrolysis to drive the release of specific ribosome assembly factors from pre-60S particles during the 60S assembly pathway[6]
NVL2 has been shown to interact with WDR7417,18, the mammalian homolog of Nsa[1], as well as a number of additional binding partners including the RNA helicase Mtr[419], nucleolar protein Nucleolin[20], ribosomal protein RPL519, and ribonucleoprotein polymerase tERT21
Summary
ATPase activity of Rix[7] is required for pre-60S biogenesis. S. cerevisiae Rix[7] is composed of 837 residues including the NTD, and the D1 and D2 AAA modules (Fig. 1a). While the D1 Walker B variant does not cause a lethal phenotype we still observed defects in ribosome assembly from the ribosome profile, suggesting that while non-essential, ATP hydrolysis by the D1 domain still plays an important role for Rix[7] function in vivo. These results, together with the yeast growth assays (Fig. 1b), reveal that the ATPase activity of Rix[7] is required for assembly of the large ribosomal subunit. WT 80S Polysomes with the D2 protomers but the α-helical lid subdomain of mouse NVL2 is in a different position (Supplementary Fig. 5c)
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