Multivalency enables unidirectional switch-like competition between intrinsically disordered proteins.

Area of Science:

• Molecular biology
• Protein-protein interactions
• Gene regulation

Background:

• Intrinsically disordered proteins (IDPs) are crucial for cellular functions, often competing for common regulatory targets.
• The transcription factor HIF-1α and its regulator CITED2 compete for binding to transcriptional coactivators CBP/p300.
• This competition acts as a molecular switch controlling gene transcription under oxygen deprivation.

Purpose of the Study:

• To elucidate the mechanistic details of how CITED2 competes with HIF-1α for binding to the TAZ1 domain.
• To determine the specific contributions of individual binding motifs within CITED2 to the competition process.
• To understand the role of protein dynamics and disorder in this allosteric molecular switch.

Main Methods:

• Solution NMR spectroscopy
• Complementary biophysical techniques
• Analysis of CITED2 mutants and truncations

Main Results:

• An N-terminal helical region of CITED2 initiates competition by forming a ternary complex, dependent on partner dynamics.
• Synergistic action of the LPEL and ϕC motifs in CITED2 enhances its binding and inhibits HIF-1α re-binding.
• Disruption of CITED2 binding regions abolishes the unidirectional nature of the competition.

Conclusions:

• Disordered proteins with multivalent motifs exhibit complex binding competition.
• CITED2 employs specific motifs to achieve unidirectional competition with HIF-1α, regulating gene expression.
• The findings offer insights into the unique mechanisms of molecular target occupancy by disordered proteins.