Talk abstracts

Talk on Saturday 11:30-11:45am submitted by Zheng Cindy Xing

Characterization of the human DEAD-box helicase DDX5

Zheng Cindy Xing (Biochemistry Department, Purdue University; Purdue Center for Cancer Research), Elizabeth Tran (Biochemistry Department, Purdue University; Purdue Center for Cancer Research)

DEAD-box proteins are a class of RNA helicases that function as RNA chaperones and RNA-protein complex (RNP) remodeling enzymes. Previous studies in our lab have revealed that the DEAD-box helicase Dbp2 in Saccharomyces cerevisiae functions in gene regulation by promoting co-transcriptional mRNP assembly and by antagonizing long non-coding RNA (lncRNA) activity (1-4). Moreover, Dbp2 is an active RNA helicase and ATPase in vitro (1, 3), suggesting that Dbp2 can modulate RNA secondary structures and remodel RNPs in vivo.

DDX5 is the mammalian ortholog of Dbp2 that plays roles in tissue differentiation and is frequently overexpressed in cancers (5). This enzyme is involved in multiple steps of RNA metabolism and transcription regulation (5), however, the mechanism of action and precise molecular roles in specific cellular processes of DDX5 remain unknown. To address these questions, we asked if DDX5 and Dbp2 are biochemically and functionally conserved. We now show that DDX5 unwinds RNA duplexes faster than Dbp2 and the mammalian specific C-terminal extension (CTE) of DDX5 is required for its higher activity. DDX5 displays slightly higher RNA binding affinity and a significantly higher on-rate than Dbp2. Moreover, DDX5 has minimal RNA annealing activities at Apo and ADP-bound state, whereas Dbp2 shows appreciable annealing activities under both conditions. Finally, DDX5 complements the overall growth and gene expression defects of dbp2∆. The mammalian/avian specific CTE of DDX5 is not required for complementation. Thus, DDX5 is an enzymatically enhanced RNA helicase that is functionally equivalent to Dbp2, suggesting a common role for this enzyme in mRNP assembly and lncRNA functions.

1. Ma WK, Cloutier SC, Tran EJ. J Mol Biol 2013; 425:3824–38.
2. Ma WK, Paudel BP, Xing Z, Sabath IG, Rueda D, Tran EJ. J Mol Biol 2016; 428:1091–106.
3. Cloutier SC, Wang S, Ma WK, Petell CJ, Tran EJ. PLoS Biol 2013; 11:32–4.
4. Cloutier SC, Wang S, Ma WK, Al Husini N, Dhoondia Z, Ansari A, Pascuzzi PE, Tran EJ. Mol Cell 2016;
5. Fuller-Pace FV. Biochimica et biophysica acta 2013; 1829(8):756-763.

Keywords: DEAD-box helicase, Biochemical conservation, Functional conservation