Molecular Architecture of SF3b and Structural Consequences of Its Cancer-Related Mutations

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The SF3b complex, a key component of the U2 small nuclear ribonucleoprotein (snRNP), is crucial for pre-mRNA splicing.
• Mutations in SF3B1/SF3b155, the largest SF3b subunit, are associated with cancer and aberrant branch site selection.

Purpose of the Study:

• To elucidate the crystal structure of the human SF3b core complex.
• To understand how SF3b155's HEAT domain conformation is stabilized.
• To map the binding sites of branch site-associated proteins within the SF3b complex.

Main Methods:

• X-ray crystallography to determine the structure of the human SF3b core complex.
• Protein-protein crosslinking to identify interacting partners and their locations.
• Structural analysis to investigate the role of SF3b155 mutations.

Main Results:

• The crystal structure reveals how SF3b155's HEAT domain is stabilized by interactions with SF3b130, SF3b10, and SF3b14b.
• p14 and U2AF65 were localized to SF3b155's HEAT-repeat superhelix, forming a composite RNA-binding platform with SF3b14b.
• Cancer-associated mutations in SF3b155 affect the tertiary structure and surface properties of the HEAT superhelix near p14 and U2AF65 binding sites.

Conclusions:

• The molecular architecture of SF3b provides insights into the spatial arrangement of cancer-related SF3b155 mutations.
• This structural understanding advances knowledge of SF3b function and the impact of mutations on splicing.
• The study reveals a composite RNA-binding platform critical for spliceosome assembly and function.