TDP-43 controls RNA structure through high affinity lattice interactions
TDP-43 is an RNA binding protein implicated in neurodegenerative disease. TDP-43 binds to GU dinucleotide repeats, which are highly abundant sequences in human RNA. Here we show TDP- 43 has one of the highest affinities and specificities measured for an RNA binding protein. Binding prevents formation of the pUG fold, an intramolecular quadruplex, and conversely pUG fold formation prevents TDP-43 binding. A rapid on-rate allows TDP-43 to capture single stranded RNA prior to folding. The protein recognizes the RNA as a 1D lattice, in which overlapping binding sites produce efficient initial binding events that interfere with subsequent interactions. This effect is partially overcome by RNA facilitated protein-protein interactions, which serve to increase the on-rate of a second TDP-43 molecule. In conjunction with all atom models, these data reveal how TDP-43 recognizes RNA repeat sequences and identify an interplay between RNA folding and protein recognition that may be relevant to human disease.