The researchers map the atomic structure of the protein complex that drive the movement of cilia

A team led by researchers from the Southwestern medical center has discovered the atomic structure of a fundamental protein complex for the function of mobile cilia, structures similar to hair that extend from the surfaces of many types of cells that generate their movement.

The findings of researchers involving radial Spoke 3 (RS3), informed in structural and molecular biology of nature, help answer some fundamental questions about how mobile cilia work and eventually they could lead to new treatments for ciliopatías, diseases in which the structure and/or function of the cilia are affected. These include primary ciliary dyskinesia, a genetic disorder that drives life that causes infertility, chronic respiratory problems, placement of inverted organs and excess brain fluid.

“Our findings reveal RS3 as a unique center that connects mechanical support with energy production and recycling in these highly preserved organizles of movement.”

Daniela Nicastro, PHD, Professor, Cell Biology, UT Southwestern

Dr. Nicastro co-led the study with Xuewu Zhang, Ph.D., Professor of Pharmacology and Biophysics, and the first author Yanhe Zhao, Ph.D., research scientist in the Nicastro laboratory.

The cilia are omnipresent in the cells, interpreting a variety of roles, explained Dr. Nicastro. While non -mobile cilia serve as sensors for chemical and mechanical signals, mobile cilia rhythmically labeled some types of cells through liquids or to move small and liquid objects in their environment and through the tissues.

Scientists have long known that the oscillatory beat of a mobile cilio is generated by thousands of molecular motor proteins called dieins. But it has not been clear how the cells coordinate their actions to beat cilia from one side to another and where the energy that this movement comes from.

To help answer these questions, UTSW researchers and other places have investigated the structures of several protein complexes that constitute the internal functioning of mobile cilia. Most of these studies have used model organisms, such as chlamydomonas unicellular green algae, which move through their aquatic habitats with two mobile cilia.

Three of these ciliary complexes make up structures called radio radios, which are repeated many times along the cilia and connect the peripheral microtubules cylinder that hold the dinein engines to a central column, so that in the cross section the radio radios resemble the radios of a wheel. While the structures of the radial complexes of Chlamydomonas 1 and 2 (RS1 and RS2) reflect those found in mammals, including humans, the RS3 algae is much shorter than the mammalian complex.

Nicastro Laboratory studies have shown that patients carrying mutations that affect RS1 and RS2, but leave intact RS3, have less severe cilioaties than where RS3 are also affected, which suggests that RS3 is exclusively important for the cilia function. However, RS3’s molecular structure had been unknown.

To solve the RS3 structure of mammals, dres. Nicastro, Zhang and Zhao and their colleagues used a variety of approaches to study RS3 of the mouse, including high-tech criolectronic microscopy (Cryo-EM) and cryoelectronic tomography, as well as proteomic and computational biology.

His research revealed that the RS3 of mammals is made of 14 proteins, 10 of which were previously unknown to be part of this complex. By matching these proteins with those in an integral mouse protein database, the researchers identified them and their functions.

Dr. Zhao said that several of the RS3 proteins are involved in placing or eliminating groups of phosphate from other proteins, a regulatory function that suspect that he and his colleagues play a role in coordinating the activity of the dinein engines. Several other proteins in this complex are involved in the generation of ATP, a fuel that cells use for energy and drives the movement of the dinein.

Together, he said, these findings suggest that the RS3 components are fundamental both to synchronize the activity of the dinein and to boost the movement of the engines in cilia.

The RS3 structure could act as a plan to design drugs that modify its activity, said Dr. Zhang. These therapies could eventually be used to treat ciliapatías such as polycystic kidney disease and discinesia of primary cilia. Researchers plan to continue investigating individual roles and protein interactions that constitute RS3 and how this structure could differ between species.

Dr. Nicastro played a fundamental role in establishing UTSW’s Cry-EM installation, which he directed until December 2019. Dr. Zhang is an academic by Virginia Murchison Linthicum in medical research.