Abstract
The cold shock domain (CSD) is an evolutionarily conserved nucleic acid binding domain that exhibits binding activity to RNA, ssDNA, and dsDNA. Mammalian CRHSP-24 contains CSD, but its structure-functional relationship has remained elusive. Here we report the crystal structure of human CRHSP-24 and characterization of the molecular trafficking of CRHSP-24 between stress granules and processing bodies in response to oxidative stress. The structure of CRHSP-24 determined by single-wavelength anomalous dispersion exhibits an α-helix and a compact β-barrel formed by five curved anti-parallel β strands. Ligand binding activity of the CSD is orchestrated by residues Ser(41) to Leu(43). Interestingly, a phosphomimetic S41D mutant abolishes the ssDNA binding in vitro and causes CRHSP-24 liberated from stress granules in vivo without apparent alternation of its localization to the processing bodies. This new class of phosphorylation-regulated interaction between the CSD and nucleic acids is unique in stress granule plasticity. Importantly, the association of CRHSP-24 with stress granules is blocked by PP4/PP2A inhibitor calyculin A as PP2A catalyzes the dephosphorylation of Ser(41) of CRHSP-24. Therefore, we speculate that CRHSP-24 participates in oxidative stress response via a dynamic and temporal association between stress granules and processing bodies.