The crystal structure of an Fe-superoxide dismutase from the hyperthermophile Aquifex pyrophilus at 1.9 Å resolution: Structural basis for thermostability

Jae Hwan Lim, Yeon Gyu Yu, Ye Sun Han, Seung Je Cho, Byung Yoon Ahn, Sung Hou Kim, Yunje Cho

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Superoxide dismutase (SOD) from Aquifex pyrophilus, a hyperthermophilic bacterium, is an extremely heat-stable enzyme that maintains about 70% of its activity after heat treatment for 60 minutes at 100°C. To understand the molecular basis of thermostability of this enzyme, we have determined the crystal structure of A. pyrophilus superoxide dismutase (Ap SOD), an Fe containing homotetrameric enzyme, at 1.9 Å resolution, and compared it with SOD structures from a mesophile and a thermophile, and other enzyme structures from other hyperthermophiles. The structure has been refined to a crystallographic X-factor (I > 2σ) of 17.0% and X-free (I > 2σ) of 19.9%. While the overall structure of the Ap SOD monomer is similar to the other SODs, significant conformational differences are observed in a highly variable loop region and the C-terminal helix. The conformational differences in these regions alter the subunit arrangement of this enzyme and generate a very compact tetramer. Structural comparisons of three SODs have revealed that Ap SOD has some stabilizing features at both the tertiary and the quaternary structural level: The Ap SOD monomer contains a large number of ion-pairs and the Ap SOD tetramer has a dramatically increased buried surface area per monomer. Comparisons of the Ap SOD structure with that of other known enzymes from hyperthermophiles reveal that the increased number of intrasubunit ion-pairs is a common feature.

Original languageEnglish
Pages (from-to)259-274
Number of pages16
JournalJournal of Molecular Biology
Issue number2
Publication statusPublished - 1997 Jul 11



  • Aquifex pyrophilus
  • Hyperthermophile
  • Ion-pair
  • Superoxide dismutase
  • Thermostability

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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