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Structural basis for the thermostability of ferredoxin from the cyanobacterium Mastigocladus laminosus.

Authors
  • Fish, Alexander
  • Danieli, Tsafi
  • Ohad, Itzhak
  • Nechushtai, Rachel
  • Livnah, Oded
Type
Published Article
Journal
Journal of molecular biology
Publication Date
Jul 15, 2005
Volume
350
Issue
3
Pages
599–608
Identifiers
PMID: 15961101
Source
Medline
License
Unknown

Abstract

Plant-type ferredoxins (Fds) carry a single [2Fe-2S] cluster and serve as electron acceptors of photosystem I (PSI). The ferredoxin from the thermophilic cyanobacterium Mastigocladus laminosus displays optimal activity at 65 degrees C. In order to reveal the molecular factors that confer thermostability, the crystal structure of M.laminosus Fd (mFd) was determined to 1.25 A resolution and subsequently analyzed in comparison with four similar plant-type mesophilic ferredoxins. The topologies of the plant-type ferredoxins are similar, yet two structural determinants were identified that may account for differences in thermostability, a salt bridge network in the C-terminal region, and the flexible L1,2 loop that increases hydrophobic accessible surface area. These conclusions were verified by three mutations, i.e. substitution of L1,2 into a rigid beta-turn ((Delta)L1,2) and two point mutations (E90S and E96S) that disrupt the salt bridge network at the C-terminal region. All three mutants have shown reduced electron transfer (ET) capabilities and [2Fe-2S] stability at high temperatures in comparison to the wild-type mFd. The results have also provided new insights into the involvement of the L1,2 loop in the Fd interactions with its electron donor, the PSI complex.

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