Fig. 4
Molecular complex of FMRP and Kv1.2. a Schematics of human FMRP structure showing tandem Agenet (Age1 and Age2) domains followed by three K Homology (KH) domains (KH0, KH1, and KH2) before ending with a long C-terminal intrinsically disordered region containing an RGG box. The cartoon representation of the crystal structure of Age1–Age2–KH0 (enclosed by dashed lines) with the red spheres showing the location of tryptophan residue. b The Age1–Age2–KH0 construct solved as an Age2-based dimer (PDB ID code 4OVA). c Left top panel shows the normalized fluorescence emission spectrum of apo-FMRP (red) and FMRP mixed with non-phosphorylated Kv1.2 C-terminal peptide (blue) or doubly-phosphorylated scrambled peptide (green). Lack of spectral changes indicates no binding. Bottom panel shows the spectral changes observed between apo-FMRP (red) and FMRP mixed with pS440 (purple), pS441 (yellow), or pS440-pS441 (cyan), all indicating a phosphorylation-mediated interaction (see text for details). Right panel shows binding profiles of pS440 (purple), pS441 (yellow), and pS440/pS441 (cyan) fitted with an FMRP dimer binding two-peptide molecules with cooperativity (for pS440) and without cooperativity (for pS441 and pS440/pS441). The binding parameters and χ2 statistics for fitting the different peptides to FMRP are given in Supplementary Table 1. d Electrostatic profiles for doubly-phosphorylated (left), non-phosphorylated (middle), and doubly-phosphorylated scrambled (right) Kv1.2 peptides. e Electrostatic profiles for the Age1–Age2–KH0 dimer. f A representative docked model of the FMRP (surface):Kv1.2 pS440/pS441 peptide (ribbon) with the phosphorylated serines shown as orange and red sticks
