title: Insight into the Dual Functions of Bacterial Enhancer-Binding Protein Rrp2 of Borrelia burgdorferi.
abstract: It is well established that the RpoN-RpoS sigma factor (σ(54)-σ(S)) cascade plays an essential role in differential gene expression during the enzootic cycle of Borrelia burgdorferi, the causative agent of Lyme disease. The RpoN-RpoS pathway is activated by the response regulator/σ(54)-dependent activator (also called bacterial enhancer-binding protein [bEBP]) Rrp2. One unique feature of Rrp2 is that this activator is essential for cell replication, whereas RpoN-RpoS is dispensable for bacterial growth. How Rrp2 controls cell replication, a function that is independent of RpoN-RpoS, remains to be elucidated. In this study, by generating a series of conditional rrp2 mutant strains, we demonstrated that the N-terminal receiver domain of Rrp2 is required for spirochetal growth. Furthermore, a D52A point mutation at the phosphorylation site within the N terminus of Rrp2 abolished cell replication. Mutation of the ATPase motif within the central domain of Rrp2 did not affect spirochetal replication, indicating that phosphorylation-dependent ATPase activity of Rrp2 for σ(54) activation is not required for cell growth. However, deletion of the C-terminal domain or a 16-amino-acid truncation of the helix-turn-helix (HTH) DNA-binding motif within the C-terminal domain of Rrp2 abolished spirochetal replication. It was shown that constitutive expression of rpoS is deleterious to borrelial growth. We showed that the essential nature of Rrp2 is not due to an effect on rpoS These data suggest that phosphorylation-dependent oligomerization and DNA binding of Rrp2 likely function as a repressor, independently of the activation of σ(54), controlling an essential step of cell replication in B. burgdorferi
  
  
  
  Bacterial enhancer-binding proteins (bEBPs) are a unique group of transcriptional activators specifically required for σ(54)-dependent gene transcription. This work demonstrates that the B. burgdorferi bEBP, Rrp2, has an additional function that is independent of σ(54), that of its essentiality for spirochetal growth, and such a function is dependent on its N-terminal signal domain and C-terminal DNA-binding domain. These findings expand our knowledge on bEBP and provide a foundation to further study the underlying mechanism of this new function of bEBP.
authors.affiliation: Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine, Wenzhou Medical University, Wenzhou, Zhejiang, China Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Yin
authors.affiliation: Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Youyun
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine, Wenzhou Medical University, Wenzhou, Zhejiang, China Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Xuwu
authors.initials: X
authors.lastname: Xiang
authors.affiliation: Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine, Wenzhou Medical University, Wenzhou, Zhejiang, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Zhejiang Provincial Center for Disease Control and Prevention, Zhejiang, China.
authors.forename: Zhang-Nv
authors.initials: ZN
authors.lastname: Yang
authors.affiliation: Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
authors.forename: Jon
authors.initials: J
authors.lastname: Blevins
authors.affiliation: Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine, Wenzhou Medical University, Wenzhou, Zhejiang, China lyl@wmu.edu.cn xfyang@iupui.edu.
authors.forename: Yongliang
authors.initials: Y
authors.lastname: Lou
authors.affiliation: Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine, Wenzhou Medical University, Wenzhou, Zhejiang, China Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA lyl@wmu.edu.cn xfyang@iupui.edu.
authors.forename: X Frank
authors.initials: XF
authors.lastname: Yang
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D025065:Borrelia burgdorferi / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D004252:DNA Mutational Analysis; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010766:Phosphorylation; D012808:Sigma Factor / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012808:Sigma Factor