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Change in structure and ligand binding properties of hyperstable cytochrome c 555 from A quifex aeolicus by domain swapping
Author(s) -
Yamanaka Masaru,
Nagao Satoshi,
Komori Hirofumi,
Higuchi Yoshiki,
Hirota Shun
Publication year - 2015
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.2627
Subject(s) - aquifex aeolicus , dimer , chemistry , crystallography , cytochrome c , heme , stereochemistry , ligand (biochemistry) , thermostability , hemeprotein , monomer , cytochrome , helix (gastropod) , crystal structure , biochemistry , biology , receptor , ecology , organic chemistry , escherichia coli , snail , mitochondrion , gene , enzyme , polymer
ABSTRACT Cytochrome c 555 from hyperthermophilic bacteria Aquifex aeolicus (AA cyt c 555 ) is a hyperstable protein belonging to the cyt c protein family, which possesses a unique long 3 10 ‐α‐3 10 helix containing the heme‐ligating Met61. Herein, we show that AA cyt c 555 forms dimers by swapping the region containing the extra 3 10 ‐α‐3 10 helix and C‐terminal α‐helix. The asymmetric unit of the crystal of dimeric AA cyt c 555 contained two dimer structures, where the structure of the hinge region (Val53–Lys57) was different among all four protomers. Dimeric AA cyt c 555 dissociated to monomers at 92 ± 1°C according to DSC measurements, showing that the dimer was thermostable. According to CD measurements, the secondary structures of dimeric AA cyt c 555 were maintained at pH 2.2–11.0. CN ‐ and CO bound to dimeric AA cyt c 555 in the ferric and ferrous states, respectively, owing to the flexibility of the hinge region close to Met61 in the dimer, whereas these ligands did not bind to the monomer under the same conditions. In addition, CN ‐ and CO bound to the oxidized and reduced dimer at neutral pH and a wide range of pH (pH 2.2–11.0), respectively, in a wide range of temperature (25–85°C), owing to the thermostability and pH tolerance of the dimer. These results show that the ligand binding character of hyperstable AA cyt c 555 changes upon dimerization by domain swapping.