title: Flexural Rigidity and Shear Stiffness of Flagella Estimated from Induced Bends and Counterbends.
abstract: Motile cilia and flagella are whiplike cellular organelles that bend actively to propel cells or move fluid in passages such as airways, brain ventricles, and the oviduct. Efficient motile function of cilia and flagella depends on coordinated interactions between active forces from an array of motor proteins and passive mechanical resistance from the complex cytoskeletal structure (the axoneme). However, details of this coordination, including axonemal mechanics, remain unclear. We investigated two major mechanical parameters, flexural rigidity and interdoublet shear stiffness, of the flagellar axoneme in the unicellular alga Chlamydomonas reinhardtii. Combining experiment, theory, and finite element models, we demonstrate that the apparent flexural rigidity of the axoneme depends on both the intrinsic flexural rigidity (EI) and the elastic resistance to interdoublet sliding (shear stiffness, ks). We estimated the average intrinsic flexural rigidity and interdoublet shear stiffness of wild-type Chlamydomonas flagella in vivo, rendered immotile by vanadate, to be EI = 840 ± 280 pN⋅μm(2) and ks = 79.6 ± 10.5 pN/rad, respectively. The corresponding values for the pf3; cnk11-6 double mutant, which lacks the nexin-dynein regulatory complex (N-DRC), were EI = 1011 ± 183 pN·μm(2) and ks = 39.3 ± 6.0 pN/rad under the same conditions. Finally, in the pf13A mutant, which lacks outer dynein arms and inner dynein arm c, the estimates were EI = 777 ± 184 pN·μm(2) and ks = 43.3 ± 7.7 pN/rad. In the two mutant strains, the flexural rigidity is not significantly different from wild-type (p > 0.05), but the lack of N-DRC (in pf3; cnk11-6) or dynein arms (in pf13A) significantly reduces interdoublet shear stiffness. These differences may represent the contributions of the N-DRCs (∼40 pN/rad) and residual dynein interactions (∼35 pN/rad) to interdoublet sliding resistance in these immobilized Chlamydomonas flagella.
authors.affiliation: Department of Engineering and Physics, University of Central Oklahoma, Edmond, Oklahoma. Electronic address: gxu@uco.edu.
authors.forename: Gang
authors.initials: G
authors.lastname: Xu
authors.affiliation: Department of Mechanical Engineering and Materials Science, Washington University in Saint Louis, Saint Louis, Missouri.
authors.forename: Kate S
authors.initials: KS
authors.lastname: Wilson
authors.affiliation: Department of Mechanical Engineering and Materials Science, Washington University in Saint Louis, Saint Louis, Missouri.
authors.forename: Ruth J
authors.initials: RJ
authors.lastname: Okamoto
authors.affiliation: Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, Missouri.
authors.forename: Jin-Yu
authors.initials: JY
authors.lastname: Shao
authors.affiliation: Department of Genetics, Washington University in Saint Louis, Saint Louis, Missouri.
authors.forename: Susan K
authors.initials: SK
authors.lastname: Dutcher
authors.affiliation: Department of Mechanical Engineering and Materials Science, Washington University in Saint Louis, Saint Louis, Missouri.
authors.forename: Philip V
authors.initials: PV
authors.lastname: Bayly
mesh_terms: D000465:Algorithms; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D004398:Dyneins / Q000235:genetics / Q000378:metabolism; D004548:Elasticity / Q000502:physiology*; D020342:Finite Element Analysis; D005407:Flagella / Q000235:genetics / Q000378:metabolism*; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D052898:Optical Tweezers; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified
chemical_list: D008868:Microtubule Proteins; D010940:Plant Proteins; C044103:tektins; D004398:Dyneins