Insight into the Tumor Suppression Mechanism from the Structure of Human Polypyrimidine Splicing Factor (PSF/SFPQ)...

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Human polypyrimidine-binding splicing factor (PSF/SFPQ) is a tumor suppressor involved in gene expression regulation and viral RNA binding.
• PSF's activity is modulated by long noncoding RNAs, including metastasis-associated transcript-1 and virus-like 30S transcript-1 (VL30-1).
• The structural basis for PSF's RNA recognition has been unclear despite knowledge of its truncated apo structure.

Purpose of the Study:

• To elucidate the structural mechanisms of PSF/SFPQ RNA recognition.
• To determine the structures of PSF alone and in complex with VL30-1 RNA.
• To understand the conformational changes and RNA-binding modes of PSF.

Main Methods:

• X-ray crystallography was used to determine the structures of a truncated PSF construct (sPSF) at 2.8 Å and 3.5 Å resolution.
• The structures were obtained for sPSF alone (apo state) and in complex with a 30-nucleotide fragment of VL30-1 RNA.
• Structural analysis focused on identifying RNA binding sites and conformational differences between the apo and complex structures.

Main Results:

• The crystal structure of the sPSF-RNA complex revealed a domain-swapped dimer with two U-specific RNA binding pockets at inter-subunit interfaces.
• These binding pockets are induced upon RNA binding and are absent in the apo structure.
• PSF transitions between low- and high-affinity RNA-binding states, suggesting a positive cooperative binding mechanism.

Conclusions:

• PSF/SFPQ recognizes RNA through induced-fit binding pockets formed at domain-swapped interfaces in a dimeric state.
• This conformational flexibility allows for high-affinity RNA binding and suggests a novel regulatory mechanism.
• The findings provide insights into PSF's role in malignancies and other human diseases.