Modulation of allostery by protein intrinsic disorder

Abstract

Allostery is an intrinsic property of many globular proteins and enzymes that is indispensable for cellular regulatory and feedback mechanisms. Recent theoretical ¹ and empirical ² observations indicate that allostery is also manifest in intrinsically disordered proteins (IDPs), which account for a significant proportion of the proteome ^{3, 4} . Many IDPs are promiscuous binders that interact with multiple partners and frequently function as molecular hubs in protein interaction networks. The adenovirus early region 1A (E1A) oncoprotein is a prime example of a molecular hub IDP ⁵ . E1A can induce drastic epigenetic reprogramming of the cell within hours after infection, through interactions with a diverse set of partners that include key host regulators like the general transcriptional coactivator CREB binding protein (CBP), its paralog p300, and the retinoblastoma protein (pRb) ^{6, 7} . Little is known about the allosteric effects at play in E1A-CBP-pRb interactions, or more generally in hub IDP interaction networks. Here, we utilized single-molecule Förster/fluorescence resonance energy transfer (smFRET) to study coupled binding and folding processes in the ternary E1A system. The low concentrations used in these high-sensitivity experiments proved essential for these studies, which are challenging due to a combination of E1A aggregation propensity and high-affinity binding interactions. Our data revealed that E1A-CBP-pRb interactions display either positive or negative cooperativity, depending on the available E1A interaction sites. This striking cooperativity switch enables fine-tuning of the thermodynamic accessibility of the ternary vs. binary E1A complexes, and may permit a context-specific tuning of associated downstream signaling outputs. Such a modulation of allosteric interactions is likely a common mechanism in molecular hub IDP function.