Mutual Enhanced Dynamic Interactions among Three Intrinsically Disordered Proteins.

The intrinsically disordered C-terminal domain (CTD) of the 4.1 proteins functions as a modular hub for interactions with diverse binding partners. Previous research has demonstrated that 4.1G-CTD associates with an intrinsically disordered region of the nuclear mitotic apparatus (NuMA) through dynamic interactions. Given that many binding partners of CTD consist of intrinsically disordered segments of membrane proteins, it is intriguing to explore whether CTD employs a similar binding mechanism with other partners. Here, we characterize the interaction between 4.1G-CTD and the third intracellular loop of dopamine receptor D2. Our findings reveal that 4.1G-CTD forms a dynamic complex with D2. Notably, the binding sites of D2 on 4.1G-CTD overlap with those of NuMA. However, D2 and NuMA can bind 4.1G-CTD simultaneously to form a ternary complex. Furthermore, bindings of D2 and NuMA exhibit mutual enhancement, suggesting a positive cooperativity between these two pairs of dynamic interactions. These insights shed new light on the mechanisms by which disordered proteins engage with multiple partners.