Sperm tails are "motorized" and need all their parts
The beat of a sperm tail is generated by a motor — a molecular motor. Each motor produces a force to power a sperm's journey to the egg. Research now shows us how each motor is powered and how it moves a sperm tail.
Cilia are those thin, protruding structures found waving on the surface of some cells. They function as both sensors receiving signals from the environment as in the lungs, and for propulsion as with sperm. They can be a single entity — sperm tail — or in multiples as on cells in our lungs. In the lungs, cilia generate flow to remove dust and pathogens from our airways. Large dynein motors (or 'outer dynein arms´, ODA) - generate a cilia's movement via the intraflagellar transport (IFT) system. Mutations in a dynein motor can result in infertility from immotile sperm, and respiratory deficiency if in the lungs.
Dyneins that move cilia are the most complex molecular motors in our body. They use ATP for energy, and are responsible for intracellular transport everywhere — including generating the force needed to make sperm move.
The research team mapped how a dynein motor is recognized by the adaptor protein ODA16 and imported into cilia via the IFT system.
Working with a crystalized structure of ODA16, they identified how a large barrel-like domain on ODA16 identifies a dynein motor; simultaneously binding the IFT complex to a cleft in that large domain as well as to a smaller domain also on ODA16.
ODA16 is truly acting like an adaptor making the large dynein and IFT complex fit together.
This new information gives scientists a better understanding of how mutations in genes can incorrectly code dynein and IFT proteins in cilia.
Research results are published in the Journal of Biological Chemistry.
Motile cilia are found on unicellular organisms such as the green alga Chlamydomonas reinhardtii, on sperm cells, and on cells that line the trachea and fallopian tubes in mammals. The motility of cilia relies on a number of large protein complexes including the force-generating outer dynein arms (ODAs). The transport of ODAs into cilia has been previously shown to require the transport adaptor ODA16 as well as the intraflagellar transport (IFT) protein IFT46, but the molecular mechanism by which ODAs are recognized and transported into motile cilia is still unclear. Here, we determined the high-resolution crystal structure of C. reinhardtii ODA16 (CrODA16) and mapped the binding to IFT46 and ODAs. The CrODA16 structure revealed a small 80-residue N-terminal domain and a C-terminal 8-bladed β-propeller domain that are both required for the association with the N-terminal 147 residues of IFT46. The dissociation constant of the IFT46-ODA16 complex was 200 nM, demonstrating that CrODA16 associates with the IFT complex with an affinity comparable to that of the individual IFT subunits. Furthermore, we show, using ODAs extracted from the axonemes of C. reinhardtii, that the C-terminal β-propeller but not the N-terminal domain of CrODA16 is required for the interaction with ODAs. These data allowed us to present an architectural model for ODA16-mediated IFT of ODAs.
The research team consists of Michael Taschner and Esben Lorentzen from the Department of Molecular Biology and Genetics, Aarhus University, Jérôme Basquin from the Max Planck Institute, Andre? Moura?o from the Helmholz Center (both in Munich, Germany) and Mayanka Awashti from Maryland University, USA.
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Mar 29, 2017 Fetal Timeline Maternal Timeline News News Archive
TOP: sperm with head (cell body) and tail (flagella or cilia) that propels it forward.
MIDDLE: dynein motors (yellow stars) being transported by intraflagellar transport (IFT).
BOTTOM: ODA16 functions as an adaptor between transport system and dynein motors.
Image Credit: Esben Lorentzen