Motor neurone link: NMR investigates proteins

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  • Published: Jul 1, 2018
  • Author: David Bradley
  • Channels: NMR Knowledge Base
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Phase separation

Nuclear magnetic resonance (NMR) spectroscopy technology has been used to investigate how two proteins important in a hereditary form of motor neurone disease, Kap-β2 importin and the FUS protein, bind to each other. The research could ultimately lead the way to a better understanding of this neurodegenerative disease. Dr Rosen pictured, from website

Nuclear magnetic resonance (NMR) spectroscopy technology has been used to investigate how two proteins important in a hereditary form of motor neurone disease (MND), Kapβ2 importin and the FUS protein, bind to each other. The research could ultimately lead the way to a better understanding of this neurodegenerative disease.

University of Texas Southwestern researchers, Yuh Min Chook, Michael Rosen, Takuya Yoshizawa, and Rustam are pioneering an area of investigation known as biological phase separation. This field looks at aspects of the organization of the cell interior and how proteins can separate out into different phases. The team has now identified in detail how some proteins bind, or fail to bind, to others– involved in cellular transport processes. When problems arise in the cell nuclei of nerve cells in the brain and spinal cord then disease can occur. For instance, proper binding and transport appear essential for the protein named FUS (fused in sarcoma), which is implicated in inherited form of MND, also known as Lou Gehrig's disease. The hereditary form accounts for 5 to 10 percent of MND cases.

Importin findings

In health, FUS binds to one of a class of nuclear transport receptors, the importin molecule called karyopherin-beta2 (Kapβ2), for instance, which transports proteins into the cell nucleus. Binding of FUS to Kapβ2 is essential for the transport of FUS into the nucleus. If FUS cannot be transported then it remains in the cytoplasm and self-associates, forming droplets of protein suspended in the cytoplasm. When mutations occur in the genetics of these proteins neurodegenerative disease called familial amyotrophic lateral sclerosis (fALS), can occur.

In 2006, Chook identified a family of nuclear localization signals, dubbed the PY-NLS, used by the FUS protein. A PY-NLS sits at one end of the elongated FUS molecule and acts like a post code for delivering the FUS protein to the nucleus. It was soon recognized as critical in the development of fALS. In 2012, importin Kapβ2 was shown to recognize the PY-NLS on the FUS protein. These discoveries allowed neuroscientists to figure out how FUS mutations lead to the aggregation of the FUS protein in the cytoplasm, but many questions remain unanswered. “The mutant FUS forms little liquid droplets within 10 minutes and these become less liquid and more solid over time, forming fibrils if the sample is left for 24 hours,” Chook explains.

"My laboratory has been working on phase separation, and Yuh Min's laboratory has done all this work on the FUS protein transport system. We wondered if the FUS droplets that we and others had observed would be affected by importin binding," Rosen adds.

Droplets and disease

It turns out that Kapβ2 blocks phase separation of FUS and that the importin’s ability to block phase separation depends on its ability to read the post code of the PY-NLS nuclear localization signal. When the post code is unreadable, as in mutated FUS, phase separation into droplets continues unimpeded, the researchers explain. NMR spectroscopy has now revealed exactly how the Kapβ2 importin binds to the FUS protein. Under normal conditions, the two bind very strongly. NMR shows reveals the dynamics in a way the crystallography never can.

“Binding at the right time, in the right place, in the right way is really important. All this transient binding appears to keep the FUS protein from interacting with itself and inhibits assembly into droplets,” Chook explains. “Those droplets are probably the initial stages of the aggregates that are a hallmark of familial ALS. If we could find a way to keep the droplets from forming, perhaps we could change the course of that neurodegenerative disease."

Related Links

Cell 2018, 173, 693: "Nuclear Import Receptor Inhibits Phase Separation of FUS through Binding to Multiple Sites"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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