MED15 prion-like domain forms a coiled-coil responsible for its amyloid conversion and propagation

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Previously, disordered to β-sheet transitions were thought to drive functional switching in Q/N-rich prions.
• Recent findings highlight the crucial role of coiled-coil (CC) regions in yeast prion domain amyloid formation.

Purpose of the Study:

• To investigate the role of CC regions in human prion-like domains (PrLDs) and their involvement in amyloid formation.
• To determine the mechanism of amyloid transition in the human MED15-PrLD and its functional implications.

Main Methods:

• Bioinformatic analysis of human PrLDs to identify CC regions and polyQ tracts.
• Biochemical assays to study MED15-PrLD homodimerization and amyloid formation.
• Cell-based assays to observe the in vivo aggregation of MED15-PrLD and its effect on endogenous MED15.

Main Results:

• Many human PrLDs, including MED15, contain CC regions overlapping with polyQ tracts.
• The human MED15-PrLD forms CC-stabilized homodimers that transition to a β-sheet amyloid state.
• Disrupting the CC fold prevents aggregation; GFP retains integrity in the amyloid state.
• MED15-PrLD expression induces cytoplasmic/perinuclear inclusions, sequestering endogenous MED15.

Conclusions:

• Coiled-coil interactions, not just disordered regions, are critical for amyloid formation in human PrLDs like MED15.
• The CC fold mediates the transition to a β-sheet amyloid state, impacting transcriptional coactivator function.
• MED15 exhibits conserved prion-like properties, suggesting novel regulatory mechanisms in transcription.