Interprotomer communication and functional asymmetry in H/ACA snoRNPs

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• H/ACA small nucleolar ribonucleoproteins (H/ACA snoRNPs) are essential for cellular processes, including RNA modification, folding, and stability.
• Dyskeratosis congenita (DC) is a rare genetic disorder linked to mutations in H/ACA proteins, affecting ribosome biogenesis and telomere maintenance.

Purpose of the Study:

• To elucidate the structural basis of H/ACA snoRNP function using cryo-electron microscopy (cryo-EM).
• To understand the coordination of pseudouridylation activity and the role of specific protein-RNA interactions.
• To investigate how mutations associated with dyskeratosis congenita impact H/ACA snoRNP function.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of endogenous insect H/ACA snoRNPs.
• Biochemical and structural analyses to characterize protein-protein and protein-RNA interactions.
• Mutational analysis to assess the impact of DC-associated mutations on pseudouridine formation.

Main Results:

• Multiple cryo-EM structures revealed endogenous insect H/ACA snoRNPs with two protomers on a two-hairpin snoRNA.
• Key interactions were characterized, explaining the prevalence of two-hairpin structures and coordinating pseudouridylation activity.
• Mutations in H/ACA proteins linked to DC were found to impair pseudouridine formation, impacting RNA modification and ribosome biogenesis.
• Coordinated structural changes in Nop10, Nhp2, and Cbf5 suggest a regulatory mechanism for H/ACA snoRNP activity.

Conclusions:

• The study provides detailed structural insights into RNA modification-competent H/ACA snoRNPs.
• The findings clarify the structural basis for H/ACA snoRNP function in essential cellular processes.
• This work links specific H/ACA snoRNP structural features and mutations to diseases like dyskeratosis congenita.