Structure-function analysis of DEAD-box helicase DDX43.

Abstract

DDX43 (DEAD-box helicase 43), also known as HAGE (helicase antigen gene), is a member of the DEAD-box protein family. It contains a K homology (KH) domain in its N terminus, a helicase core domain in its C terminus, and a flexible linker domain in between. DDX43 expression is low or undetectable in normal tissue, but is overexpressed in many tumors; therefore, it is considered a potential target molecule for cancer therapy. We, along with other groups, have shown that DDX43 is an ATP-dependent RNA and DNA helicase, and the KH domain is required for its ATPase and unwinding activity. Electrophoretic mobility shift assay (EMSA), SELEX (systematic evolution of ligands by exponential enrichment), chromatin immunoprecipitation (ChIP)-seq, crosslinking immunoprecipitation (CLIP)-seq, and nuclear magnetic resonance (NMR) showed that the KH domain prefers to bind pyrimidine-rich ssDNA and ssRNA, such as TTGT in the promoter regions of genes. Moreover, the KH domain facilitates the substrate specificity and processivity of the DDX43 helicase. No animal model has been generated for DDX43; cellular studies have revealed that DDX43 has roles in piRNA amplification, tumorigenesis, RAS signaling, and innate immunity. Structural and functional studies of DDX43 will not only advance our understanding of DEAD-box helicases and KH domains, but also shed light on the application of DDX43 as therapeutics, where its key binding sites can be targeted by small molecules and natural products as an alternative approach in treating DDX43 overexpressed cancers.