title: Structure of Trypanosoma brucei flagellum accounts for its bihelical motion.
abstract: Trypanosoma brucei is a parasitic protozoan that causes African sleeping sickness. It contains a flagellum required for locomotion and viability. In addition to a microtubular axoneme, the flagellum contains a crystalline paraflagellar rod (PFR) and connecting proteins. We show here, by cryoelectron tomography, the structure of the flagellum in three bending states. The PFR lattice in straight flagella repeats every 56 nm along the length of the axoneme, matching the spacing of the connecting proteins. During flagellar bending, the PFR crystallographic unit cell lengths remain constant while the interaxial angles vary, similar to a jackscrew. The axoneme drives the expansion and compression of the PFR lattice. We propose that the PFR modifies the in-plane axoneme motion to produce the characteristic trypanosome bihelical motility as captured by high-speed light microscope videography.
authors.affiliation: National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Alexey Y
authors.initials: AY
authors.lastname: Koyfman
authors.forename: Michael F
authors.initials: MF
authors.lastname: Schmid
authors.forename: Ladan
authors.initials: L
authors.lastname: Gheiratmand
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Fu
authors.forename: Htet A
authors.initials: HA
authors.lastname: Khant
authors.forename: Dandan
authors.initials: D
authors.lastname: Huang
authors.forename: Cynthia Y
authors.initials: CY
authors.lastname: He
authors.forename: Wah
authors.initials: W
authors.lastname: Chiu
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D020285:Cryoelectron Microscopy; D005407:Flagella / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D006801:Humans; D008954:Models, Biological; D008958:Models, Molecular; D009068:Movement / Q000502:physiology; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D014346:Trypanosoma brucei brucei / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D015800:Protozoan Proteins; C045519:paraflagellar rod proteins, Trypanosoma brucei