The Structural Characterization of AtLaRP6a C‐Terminal Domain

Abstract

The La related proteins (LaRPs) are a superfamily of RNA binding proteins characterized by a conserved sequence called the La Module. This domain is composed of two distinct regions, the La Motif (LAM) and an RNA recognition motif (RRM), which form a functional RNA binding unit. The LaRP6 subfamily is characterized by a putative protein‐protein interaction motif in the C‐terminus, called the LAM‐ and S1 associated (LSA) motif. Interestingly, plants express three paralogs of LaRP6 (A, B, and C). We have recombinantly expressed and purified the LaRP6A protein from the plant model organism Arabidopsis thaliana, to compare the plant LaRP6A to the LaRP6 proteins of vertebrate organisms for the purpose of probing differences in structure and function. Previous work in our lab suggested that the C‐terminal domain of AtLaRP6A is intrinsically disordered. In this study, we have recombinantly expressed and purified only the C‐terminal domain. Biochemical and biophysical analyses, including analytical size exclusion chromatography, limited proteolysis, and circular dichroism, all support the prediction that the CTD is an intrinsically disordered region. This work provides a foundation to further study the role of the CTD in regulatory protein‐protein interactions to better understand the biological role for LaRP6.