Structural insight of human DEAD‐box protein rck/p54 into its substrate recognition with conformational changes

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Abstract
Human rck/p54, a product of the gene cloned at the breakpoint of t(11; 14) (q23;q32) chromosomal translocation on 11q23 in B‐cell lymphoma, is a member of the DEAD‐box RNA helicase family. Here, the crystal structure of Nc‐rck/p54, the N‐terminal core domain of rck/p54, revealed that the P‐loop in motif I formed a closed conformation, which was induced by Asn131, a residue unique to the RCK subfamily. It appears that ATP does not bind to the P‐loop. The results of dynamic light scattering revealed to ATP‐induced conformational change of rck/p54. It was demonstrated that free rck/p54 is a distended molecule in solution, and that the approach between N‐terminal core and C‐terminal domains for ATP binding would be essential when unwinding RNA. The results from helicase assay using electron micrograph, ATP hydrolytic and luciferase assay showed that c‐myc IRES RNA, whose secondary structure regulates IRES‐dependant translation, was unwound by rck/p54 and indicated that it is a good substrate for rck/p54. Over‐expression of rck/p54 in HeLa cells caused growth inhibition and cell cycle arrest at G2/M with down‐regulation of c‐myc expression. These findings altogether suggest that rck/p54 may affect the IRES‐dependent translation of c‐myc even in the cells.