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MDA5 disease variant M854K prevents ATP-dependent structural discrimination of viral and cellular RNA

Qin Yu1,2,3, Alba Herrero Del Valle1,2, Rahul Singh1,2

  • 1Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0QH, UK.

Nature Communications
|November 19, 2021
PubMed

Insights

Mutations in MDA5, a sensor of viral RNA, can cause autoinflammatory disease. The M854K variant disrupts MDA5 function by inhibiting its ATPase activity, leading to inappropriate immune activation by self-RNA.

Area of Science:

  • Innate immunity
  • Molecular biology
  • Structural biology

Background:

  • Innate immune responses to viral RNA are crucial for defense.
  • MDA5 recognizes long cytosolic double-stranded RNA (dsRNA).
  • MDA5 ATPase activity is key for dsRNA binding selectivity; mutations can cause autoinflammatory disease.

Purpose of the Study:

  • To elucidate how the disease-associated MDA5 variant M854K affects MDA5-dsRNA recognition.
  • To understand the structural and mechanistic basis of MDA5 dysfunction in autoinflammatory disease.

Main Methods:

  • Cryo-electron microscopy (CryoEM) to determine structures of MDA5-dsRNA filaments.
  • Biochemical assays to assess ATPase activity and RNA binding.
  • Analysis of the M854K variant's impact on MDA5 conformation and function.

Main Results:

  • M854K MDA5 exhibits constitutive interferon signaling activation, independent of exogenous RNA.
  • The M854K variant lacks ATPase activity and shows enhanced binding to synthetic dsRNA.
  • CryoEM structures reveal that M854K disrupts key ATPase cycle steps (RNA footprint expansion, helical twist modulation) through polar bond formation by K854.
  • M854K inhibits ATP-dependent RNA proofreading via an allosteric mechanism, enabling signaling on endogenous RNAs.

Conclusions:

  • The M854K mutation impairs MDA5's RNA selectivity and proofreading capabilities.
  • Dysfunctional MDA5, due to mutations like M854K, can lead to autoinflammatory disease by recognizing self-RNAs.
  • This study provides critical insights into MDA5-dsRNA recognition mechanisms in both health and disease.

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