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The giant mimivirus 1.2 Mb genome is elegantly organized into a 30-nm diameter helical protein shield

Alejandro Villalta1, Alain Schmitt1, Leandro F Estrozi2

  • 1Aix-Marseille University, Centre National de la Recherche Scientifique, Information Génomique & Structurale, Unité Mixte de Recherche 7256 (Institut de Microbiologie de la Méditerranée, FR3479, IM2B), Marseille, France.

Elife
|July 28, 2022
PubMed

Insights

Mimivirus giant viruses package their DNA genome within a unique helical protein shell made of oxidoreductases. This structure protects the genome and primes it for transcription upon host entry.

Area of Science:

  • Virology
  • Structural Biology
  • Genomics

Background:

  • Mimivirus, a giant dsDNA virus, has a large genome (1.2 Mb) housed within an icosahedral capsid.
  • The internal organization and packaging of the Mimivirus genome remain poorly understood.

Purpose of the Study:

  • To elucidate the supramolecular organization of the Mimivirus genome and its protective shell.
  • To investigate the protein composition and structural arrangement of the viral nucleoid.

Main Methods:

  • Cryo-electron microscopy (cryo-EM)
  • Cryo-electron tomography (cryo-ET)
  • Proteomics analysis

Main Results:

  • The Mimivirus genome is organized into left-handed super-helices within the capsid.
  • A ~30-nm diameter helical protein shell, composed of GMC-type oxidoreductases, encases the genome.
  • These oxidoreductases also form the glycosylated capsid fibrils.
  • The genome's central channel accommodates oxidative stress proteins and RNA polymerase subunits.

Conclusions:

  • Mimivirus employs an efficient genome packaging strategy using a single protein type for both the internal shell and external fibrils.
  • This organization facilitates rapid genome transcription upon release into the host cytoplasm.
  • The findings offer insights into viral evolution and genome management in giant viruses.
Keywords:
cryo-EMcryo-ETgiant virusinfectious diseasemicrobiologymimivirusmolecular biophysicsproteomicsstructural biologyviral dsDNA organizationviruses

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