MD and Docking Studies Reveal That the Functional Switch of CYFIP1 is Mediated by a Butterfly-like Motion.

Cytoplasmic FMRP interacting protein 1 (CYFIP1), also known as specifically RAC1 activated protein 1 (Sra1), plays a dual role: together with fragile X mental retardation protein (FMRP) and eIF4E it forms a complex that inhibits mRNA translation, while together with WAVE1, NCKAP1, ABI2, and HSPC300 it forms the WAVE regulatory complex (WRC) that upon RAC1 activation initiates actin polymerization. Here we performed a molecular dynamics (MD) simulation on CYFIP1 extracted from the known WRC structure, which shows that, in the absence of its WRC partners, a butterfly-like motion brings the two ends of CYFIP1 closer together, enabling the interaction with eIF4E. Our MD simulation is supported by available data showing that binding of CYFIP1 to eIF4E and binding to the WRC are mutually exclusive and that there is fluorescence resonance energy transfer between the N- and C-termini of CYFIP1. The differential interaction of RAC1-GTP with the two CYFIP1 structures predicts that RAC1 is directly responsible for the switch between these conformations.