title: Structural basis for the thermostability of ferredoxin from the cyanobacterium Mastigocladus laminosus.
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.
authors.affiliation: The Department of Plant Sciences, The Wolfson Centre for Applied Structural Biology, The Institute of Life Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel.
authors.forename: Alexander
authors.initials: A
authors.lastname: Fish
authors.forename: Tsafi
authors.initials: T
authors.lastname: Danieli
authors.forename: Itzhak
authors.initials: I
authors.lastname: Ohad
authors.forename: Rachel
authors.initials: R
authors.lastname: Nechushtai
authors.forename: Oded
authors.initials: O
authors.lastname: Livnah
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004583:Electrons; D005288:Ferredoxins / Q000737:chemistry*; D006358:Hot Temperature; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012492:Salts / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D013696:Temperature
chemical_list: D018076:DNA, Complementary; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D012492:Salts; D006859:Hydrogen; D010100:Oxygen