Interaction with Cu²⁺ disrupts the RNA binding affinities of RNA recognition motif containing protein

The glycine-rich proteins (GRP) containing RNA recognition motifs (RRM) are involved in the regulation of transcriptional and/or post-transcriptional events. Previous studies have established that GRP162 plays an important role in the restoration of fertility in Honglian cytoplasmic male sterile (HL-CMS) rice. In this study, the ion binding properties of rGRP162 were tested by isothermal titration calorimetry (ITC) and electrophoretic mobility shift assay (EMSA) was performed to test the interaction. Circular dichroism (CD) was carried out to detect the alteration of secondary structure in the presence and absence of Cu(2+). Furthermore, two RRM containing proteins, AtRBP45A and AtRBP47A, were expressed to validate the interaction. Results showed Cu(2+) and Fe(3+) bound GRP162, whereas Ca(2+), Mn(2+), Mg(2+) and K(+) did not. EMSA confirmed that interaction with Cu(2+) interrupted the biological activity of GRP162 by disrupting the secondary structure of the protein based on the results of CD. Moreover, the RNA binding activities of rAtRBP45A and rAtRBP47A were also impaired in the presence of Cu(2+). Data suggest that Cu(2+) in excess may disrupt RNA-binding proteins containing RRM that are essential for post-transcriptional regulation and may impair the development of plants or animals.