Large-scale ratcheting in a bacterial DEAH/RHA-type RNA helicase that modulates antibiotics susceptibility Lena M. Grassa, Jan Wollenhauptb, Tatjana Barthela,b, Iwan Parfentevc, Henning Urlaubc,d, Bernhard Lolla, Eberhard Klaucke, Haike Antelmanne, and Markus C. Wahla,b,1 aLaboratory of Structural Biochemistry, Institute of Chemistry and Biochemistry, Freie Universität Berlin, D-14195 Berlin, Germany; bMacromolecular Crystallography, Helmholtz-Zentrum Berlin für Materialien und Energie, D-12489 Berlin, Germany; cBioanalytical Mass Spectrometry, Max-Planck-Institut für biophysikalische Chemie, D-37077 Göttingen, Germany; dBioanalytics, Institute of Clinical Chemistry, Universitätsmedizin Göttingen, D-37075 Göttingen, Germany; and eMicrobiology, Institute of Biology, Freie Universität Berlin, D-14195 Berlin, Germany Edited by Robert Huber, Max Planck Institute of Biochemistry, Planegg-Martinsried, Germany, and approved June 14, 2021 (received for review January 10, 2021) Many bacteria harbor RNA-dependent nucleoside-triphosphatases by α-helices and harbor up to about a dozen conserved sequence of the DEAH/RHA family, whose molecular mechanisms and cellular motifs that are involved in NTP binding/hydrolysis, RNA/RNP functions are poorly understood. Here, we show that the Escheri- binding/remodeling, and functionally connecting these activities chia coli DEAH/RHA protein, HrpA, is an ATP-dependent 3 to 5′ RNA (17, 18). Additional domains and regions can modulate the func- helicase and that the RNA helicase activity of HrpA influences bac- tions of the RecA cores in diverse ways (27). terial survival under antibiotics treatment. Limited proteolysis, crys- Based on the presence and conservation of particular motifs, tal structure analysis, and functional assays showed that HrpA the presence of auxiliary domains and the biochemical activities, contains an N-terminal DEAH/RHA helicase cassette preceded by a nucleic acid–dependent NTPases have been divided into six su- unique N-terminal domain and followed by a large C-terminal re- perfamilies (SFs) (17, 18). The vast majority of known rdNTPases gion that modulates the helicase activity. Structures of an expanded belong to SF2. SF2 enzymes have been further subdivided into HrpA helicase cassette in the apo and RNA-bound states in combi- several families and subfamilies. rdNTPases that exhibit an nation with cross-linking/mass spectrometry revealed ratchet-like Asp-Glu-Ala-Asp or Asp-Glu-variable-His sequence in their motifs domain movements upon RNA engagement, much more pronounced belong to the DEAD-box and DEAH/RHA families of SF2, re- than hitherto observed in related eukaryotic DEAH/RHA enzymes. spectively (17, 18). The molecular mechanisms of DEAD-box BIOCHEMISTRY Structure-based functional analyses delineated transient interdomain proteins have been thoroughly studied in both prokaryotes and contact sites that support substrate loading and unwinding, suggest- eukaryotes (3, 4, 17, 18, 28), whereas our present knowledge about ing that similar conformational changes support RNA translocation. DEAH/RHA protein mechanisms has been predominantly de- Consistently, modeling studies showed that analogous dynamic intra- rived from studies of eukaryotic enzymes (29, 30). molecular contacts are not possible in the related but helicase-inactive Structural analyses of eukaryotic DEAH/RHA proteins, such as RNA-dependent nucleoside-triphosphatase, HrpB. Our results indicate Chaetomium thermophilum Prp22 (31), Saccharomyces cerevisiae that HrpA may be an interesting target to interfere with bacterial Prp43 (32–34), Drosophila melanogaster MLE (35), or Mus musculus tolerance toward certain antibiotics and suggest possible interfering Dhx37 (36) have revealed a core comprising two RecA-like do- strategies. mains with auxiliary winged helix (WH), helical bundle/ratchet RNA-dependent NTPase/RNA helicase | co-/posttranscriptional gene Significance regulation | antibiotics resistance | X-ray crystallography | structural biology Bacteria rely on RNA-binding and RNA-remodeling proteins to regulate gene expression posttranscriptionally. RNA-dependent o cope with fast-changing environmental conditions, bacteria nucleoside-triphosphatases of the DEAH/RHA family constitute Trapidly adjust their cellular proteomes. As changes in protein important posttranscriptional gene regulatory proteins in bacte- levels often do not perfectly correlate with changes in messenger ria, but their molecular mechanisms are presently poorly under- RNA (mRNA) levels, gene expression programs are not only stood. Here, we show that the DEAH/RHA protein, HrpA, from regulated on the transcriptional but also on the posttranscrip- Escherichia coli is an RNA helicase and that its helicase activity is tional level (1). Noncoding RNAs and RNA-binding proteins required to modulate bacterial survival under diverse antibiotics (RBPs) are the main mediators of posttranscriptional gene regu- treatments. HrpA crystal structures in different functional states, lation in bacteria (2). RNA-dependent nucleoside-triphosphatases cross-linking/mass spectrometry, and structure-guided functional (rdNTPases) are a major group of posttranscriptionally active analyses indicate that alternative interdomain contacts facilitate RBPs that can impact, among others, RNA processing, RNA large-scale domain movements that are required for RNA bind- decay, ribosome biogenesis, and translation initiation by binding – ing, translocation, and unwinding. Our findings portray HrpA as a and remodeling RNAs and RNA protein complexes (RNPs) (3, 4). molecular ratchet that translocates single-stranded RNA through Thereby, they can influence quorum sensing and biofilm formation a central orifice, thereby displacing a complementary strand. (5), mediate adaptation to diverse stress conditions (6–10), modulate – virulence and infectivity (11 13), alter susceptibility of bacteria to Author contributions: H.U., H.A., and M.C.W. designed research; L.M.G., J.W., T.B., I.P., antimicrobials (14, 15), and buffer adverse effects of mutations (16). B.L., and E.K. performed research; L.M.G., J.W., T.B., I.P., H.U., B.L., E.K., H.A., and M.C.W. In vitro, many rdNTPases can unwind RNA duplexes in an analyzed data; and L.M.G. and M.C.W. wrote the paper. NTP-dependent (most often ATP-dependent) manner [i.e., act The authors declare no competing interest. as RNA helicases (17, 18)]. However in vivo, some of these en- This article is a PNAS Direct Submission. zymes can also anneal RNAs (19, 20), stably clamp RNAs (21), This open access article is distributed under Creative Commons Attribution-NonCommercial- initiate buildup of higher-order RNPs (22, 23), or displace RNA- NoDerivatives License 4.0 (CC BY-NC-ND). bound proteins (24) or RNA-bound RNPs (25, 26) from RNAs. 1To whom correspondence may be addressed. Email: [email protected]. All of these activities depend on the presence of RecA-like NTP- This article contains supporting information online at https://www.pnas.org/lookup/suppl/ binding/NTPase domains that form the rdNTPase cores. The doi:10.1073/pnas.2100370118/-/DCSupplemental. RecA domains comprise parallel-stranded β-sheets surrounded Published July 21, 2021. PNAS 2021 Vol. 118 No. 30 e2100370118 https://doi.org/10.1073/pnas.2100370118 | 1of12 Downloaded by guest on October 3, 2021 (HB), and oligonucleotide/oligosaccharide-binding (OB) domains (chloramphenicol and tetracyclin), or cell wall synthesis (ampicillin). forming a ring-like arrangement with the core domains. In DEAH/ In the absence of antibiotics, the hrpA mutant showed a similar RHA proteins that act as RNA helicases, this architecture is re- survival as the WT strain, suggesting that ecHrpA is not essential for quired for processive RNA unwinding (37, 38). RNA unwinding viability or that it is redundant. In the presence of rifampicin, hrpA involves translocation of a loading strand of an RNA duplex across mutant cells showed an enhanced survival compared to WT cells the RecA domains, with the helicase moving in 3′ to 5′ direction (Fig. 1A). However, the hrpA mutant was strongly impaired in on the loading strand and with concomitant exclusion of the dis- survival in the presence of chloramphenicol, tetracyclin, or am- placed strand (37, 38). In the process, the RecA-like domains pre- picillin (Fig. 1A). These results show that the hrpA gene bestows dominantly contact the sugar-phosphate backbone of the loading on E. coli increased tolerance toward certain antibiotics that strand and thus do not generally provide substrate specificity (18). target the translation machinery or cell wall synthesis but can also Details of the translocation and unwinding mechanisms can differ in cause higher sensitivity toward other antibiotics, such as the RNA different DEAH/RHA enzymes (30) due to differences in particular polymerase inhibitor rifampicin. motifs or due to specific insertions or terminal extensions in some of these proteins (33, 35, 39–41). ecHrpA Is an RNA Helicase with 3 to 5′ Directionality. ecHrpA is a In bacteria, DEAH/RHA NTPases have been divided into three putative RNA helicase (42). However, we and others have recently subfamilies: HrpA-like, HrpB-like, and Z5898-like enzymes (3, 4), investigated the related ecHrpB protein, whose orthologs had also referring to the corresponding Escherichia coli factors. The cellular been tentatively annotated as RNA helicases (45); while ecHrpB functions and RNA-related activities of these proteins are still exhibited RNA-stimulated NTPase activity, it failed to unwind