KAIST

<(From Left) Professor Ji-Joon Song, Ph.D candidate Jaesung Kim, Dr. Hyeongju Kim of KAIST’s Department of Biological Sciences>

Huntington’s disease is a rare genetic disorder and a representative neurodegenerative disease, characterized by loss of motor control, cognitive decline, and psychiatric problems. An international research team has discovered that the “huntingtin protein,” the causal protein of Huntington’s disease (whose mutations are the direct cause of the disease), also performs a new function: directly organizing the cytoskeleton, the fine structural framework inside cells. This discovery is expected to contribute not only to understanding the pathogenic mechanism of Huntington’s disease, but also to research on neurodevelopmental disorders such as Alzheimer’s disease and Parkinson’s disease, as well as muscle- or mobility-related diseases such as muscular dystrophy.

KAIST (President Kwang Hyung Lee) announced on September 30 that a research team led by Professor Ji-Joon Song of the Department of Biological Sciences, in collaboration with the Institute of Science and Technology Austria (ISTA), Sorbonne University/Paris Brain Institute, and the Swiss Federal Institute of Technology Lausanne (EPFL), has uncovered—through cryo-electron microscopy (cryo-EM) and cell biology methods—the structural principle by which the huntingtin protein arranges cytoskeletal microfilaments (F-actin) into bundles.

Until now, the huntingtin protein was known only to “use” the cytoskeleton, being involved in vesicle transport or microtubule-based transport. The team, however, demonstrated that huntingtin physically organizes the cytoskeleton itself. This study is considered the first in the world to prove this new role of the huntingtin protein at the molecular level.

The researchers confirmed that huntingtin binds directly to cytoskeletal microfilaments (F-actin), and that pairs of huntingtin proteins bundle the cytoskeleton into arrays at intervals of about 20 nanometers.

Such cytoskeletal bundles play a crucial role in the development of neural connectivity. Indeed, structural development of neurons was found to be impaired in nerve cells deficient in the huntingtin protein.

<Elucidation of the Mechanism of Cytoskeletal Microfilament Bundle Formation by Huntingtin Protein and Its Impact on Neuronal Development>

First author Jaesung Kim, a PhD candidate at KAIST, stated, “This study provides a new perspective for understanding the molecular mechanism of the huntingtin protein, the cause of an incurable disease that has long remained a mystery.”

Professor Ji-Joon Song of KAIST’s Department of Biological Sciences explained, “This achievement not only provides an important clue to understanding the pathogenic mechanism of Huntington’s disease, but is also expected to have a far-reaching impact on research into cytoskeleton-related diseases,” and added that “it opens new avenues for exploring the role of the huntingtin protein in diverse biological phenomena such as cell division, migration, and mechanical signal transduction.”

This research was conducted with Jaesung Kim (PhD candidate, KAIST), Hyeongju Kim (now at Harvard University), Rémi Carpentier (Paris Brain Institute), Mariacristina Capizzi (Paris Brain Institute), and others as co-first authors, and was published on September 19 in Science Advances, a sister journal of Science.

※ Paper title: “Structure of the Huntingtin F-actin complex reveals its role in cytoskeleton organization,” DOI: https://doi.org/10.1126/sciadv.adw4124
※ Co-corresponding authors: Ji-Joon Song (KAIST), Florian Schur (ISTA), and Sandrine Humbert (Sorbonne University/Paris Brain Institute).

This research was supported by the Ministry of Health and Welfare’s Global Research Collaboration Program (Korea–Switzerland Biohealth International Joint Research) and the Korea–Austria Cooperation Program.