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Title
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Heme packing motifs revealed by the crystal structure of the tetra-heme cytochrome c554 from Nitrosomonas europaea.
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Authors
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T.M.Iverson,
D.M.Arciero,
B.T.Hsu,
M.S.Logan,
A.B.Hooper,
D.C.Rees.
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Ref.
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Nat Struct Biol, 1998,
5,
1005-1012.
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PubMed id
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Abstract
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Cytochrome c554 (cyt c554), a tetra-heme cytochrome from Nitrosomonas europaea,
is an essential component in the biological nitrification pathway. In N.
europaea, ammonia is converted to hydroxylamine, which is then oxidized to
nitrite by hydroxylamine oxidoreductase (HAO). Cyt c554 functions in the latter
process by accepting pairs of electrons from HAO and transferring them to a
cytochrome acceptor. The crystal structure of cyt c554 at 2.6 A resolution shows
a predominantly alpha-helical protein with four covalently attached hemes. The
four hemes are arranged in two pairs such that the planes of the porphyrin rings
are almost parallel and overlapping at the edge; corresponding heme arrangements
are observed in other multi-heme proteins. Striking structural similarities are
evident between the tetra-heme core of cyt c554 and hemes 3-6 of HAO, which
suggests an evolutionary relationship between these redox partners.
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