title: Neisseria gonorrhoeae RecQ helicase HRDC domains are essential for efficient binding and unwinding of the pilE guanine quartet structure required for pilin antigenic variation.
abstract: The strict human pathogen Neisseria gonorrhoeae utilizes homologous recombination to antigenically vary the pilus, thus evading the host immune response. High-frequency gene conversion reactions between many silent pilin loci and the expressed pilin locus (pilE) allow for numerous pilus variants per strain to be produced from a single strain. For pilin antigenic variation (Av) to occur, a guanine quartet (G4) structure must form upstream of pilE. The RecQ helicase is one of several recombination or repair enzymes required for efficient levels of pilin Av, and RecQ family members have been shown to bind to and unwind G4 structures. Additionally, the vast majority of RecQ helicase family members encode one "helicase and RNase D C-terminal" (HRDC) domain, whereas the N. gonorrhoeae RecQ helicase gene encodes three HRDC domains, which are critical for pilin Av. Here, we confirm that deletion of RecQ HRDC domains 2 and 3 causes a decrease in the frequency of pilin Av comparable to that obtained with a functional knockout. We demonstrate that the N. gonorrhoeae RecQ helicase can bind and unwind the pilE G4 structure. Deletion of the RecQ HRDC domains 2 and 3 resulted in a decrease in G4 structure binding and unwinding. These data suggest that the decrease in pilin Av observed in the RecQ HRDC domain 2 and 3 deletion mutant is a result of the enzyme's inability to efficiently bind and unwind the pilE G4 structure.
authors.affiliation: Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Laty A
authors.initials: LA
authors.lastname: Cahoon
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Manthei
authors.forename: Ella
authors.initials: E
authors.lastname: Rotman
authors.forename: James L
authors.initials: JL
authors.lastname: Keck
authors.forename: H Steven
authors.initials: HS
authors.lastname: Seifert
mesh_terms: D000940:Antigenic Variation / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D036781:Fimbriae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005454:Fluorescence Polarization; D009344:Neisseria gonorrhoeae / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D053484:RecQ Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C074063:pilE protein, Neisseria gonorrhoeae; D036781:Fimbriae Proteins; D053484:RecQ Helicases