title: Suppression of subtelomeric VSG switching by Trypanosoma brucei TRF requires its TTAGGG repeat-binding activity.
abstract: Trypanosoma brucei causes human African trypanosomiasis and regularly switches its major surface antigen, VSG, in the bloodstream of its mammalian host to evade the host immune response. VSGs are expressed exclusively from subtelomeric loci, and we have previously shown that telomere proteins TbTIF2 and TbRAP1 play important roles in VSG switching and VSG silencing regulation, respectively. We now discover that the telomere duplex DNA-binding factor, TbTRF, also plays a critical role in VSG switching regulation, as a transient depletion of TbTRF leads to significantly more VSG switching events. We solved the NMR structure of the DNA-binding Myb domain of TbTRF, which folds into a canonical helix-loop-helix structure that is conserved to the Myb domains of mammalian TRF proteins. The TbTRF Myb domain tolerates well the bulky J base in T. brucei telomere DNA, and the DNA-binding affinity of TbTRF is not affected by the presence of J both in vitro and in vivo. In addition, we find that point mutations in TbTRF Myb that significantly reduced its in vivo telomere DNA-binding affinity also led to significantly increased VSG switching frequencies, indicating that the telomere DNA-binding activity is critical for TbTRF's role in VSG switching regulation.
authors.affiliation: Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA.
authors.forename: Sanaa E
authors.initials: SE
authors.lastname: Jehi
authors.affiliation: Department of Applied Biology and Chemical Technology, State Key Laboratory of Chirosciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P. R. China The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen, P.R. China.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Li
authors.affiliation: Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA.
authors.forename: Ranjodh
authors.initials: R
authors.lastname: Sandhu
authors.affiliation: Division of Life Science, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P. R. China.
authors.forename: Fei
authors.initials: F
authors.lastname: Ye
authors.affiliation: Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA.
authors.forename: Imaan
authors.initials: I
authors.lastname: Benmerzouga
authors.affiliation: Division of Life Science, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P. R. China.
authors.forename: Mingjie
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Applied Biology and Chemical Technology, State Key Laboratory of Chirosciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P. R. China yanxiang.zhao@polyu.edu.hk.
authors.forename: Yanxiang
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH 44106, USA Department of Molecular Genetics, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA The Rockefeller University, New York, NY 10065, USA b.li37@csuohio.edu.
authors.forename: Bibo
authors.initials: B
authors.lastname: Li
mesh_terms: D000940:Antigenic Variation; D004247:DNA / Q000378:metabolism; D019077:Helix-Turn-Helix Motifs; D009154:Mutation; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000276:immunology*; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000276:immunology*
chemical_list: D015800:Protozoan Proteins; D034501:Telomere-Binding Proteins; D014643:Variant Surface Glycoproteins, Trypanosoma; D004247:DNA