RNA Chaperone Activity of the RRM2 Domain of Human La

Genuine La proteins are abundant RNA binding factors that primarily facilitate maturation of nascent precursor RNAs in eukaryotes. Chaperone activity is a conserved feature in the La superfamily, yet the structural basis for this activity remains obscure. RNAs bound by human La (hLa) primarily make contacts with the conserved La module in the N-terminal domain. However, a role for the non- canonical RRM2 fold in the C-terminal domain (CTD) has been proposed recently. Using gel shift assays, nuclear magnetic resonance (NMR) spectroscopy, and circular dichroism (CD) spectroscopy, we aim to understand hLa’s uncharacterized RRM2 dependent binding. Our results demonstrate that the RRM2 relies on non-canonical features including a subsequent disordered C terminal to bind RNA. Consequently, we predict that this region becomes ordered to facilitate hLa’s chaperone function. Taken together, these data support a model for disordered regions in chaperone activity and expand our understanding of La’s function.