Crystal structures of the N-terminal domain of the Staphylococcus aureus DEAD-box RNA helicase CshA and its complex with AMP

CshA is a DEAD-box RNA helicase that belongs to the DExD/H-box family of proteins, which generally have an RNA-dependent ATPase activity. In Staphylococcus aureus, CshA was identified as a component of the RNA degradosome and plays important roles in RNA turnover. In this study, the crystal structures of the N-terminal RecA-like domain 1 of S. aureus CshA (SaCshA^R1) and of its complex with AMP (SaCshA^R1–AMP) are reported at resolutions of 1.5 and 1.8 Å, respectively. SaCshA^R1 adopts a conserved α/β RecA-like structure with seven parallel strands surrounded by nine α-helices. The Q motif and motif I are responsible for the binding of the adenine group and phosphate group of AMP, respectively. Structure comparison of SaCshA^R1–AMP and SaCshA^R1 reveals that motif I undergoes a conformational change upon AMP binding. Isothermal titration calorimetry assays further conformed the essential roles of Phe22 in the Q motif and Lys52 in motif I for binding ATP, indicating a conserved substrate-binding mechanism in SaCshA compared with other DEAD-box RNA helicases.