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J Biol Chem, Vol. 273, Issue 20, 12006-12016, May 15, 1998
Cloning and Expression in Escherichia coli of the
Cytochrome c552 Gene from Thermus
thermophilus HB8
EVIDENCE FOR GENETIC LINKAGE TO AN ATP-BINDING CASSETTE PROTEIN
AND INITIAL CHARACTERIZATION OF THE cycA GENE PRODUCTS
J. Andrew
Keightley §,
Donita
Sanders ,
Thomas R.
Todaro ,
Andrzej
Pastuszyn¶, and
James A.
Fee §
From the Department of Biology, University of
California at San Diego, La Jolla, California 92093, the
§ Los Alamos National Laboratory, Los Alamos, New Mexico
87545, and the ¶ Protein Chemistry Laboratory and Department of
Biochemistry and Molecular Biology, University of New Mexico,
Albuquerque, New Mexico 87131-5221
We report sequence of Thermus
thermophilus HB8 DNA containing the gene (cycA) for
cytochrome c552 and a gene (cycB)
encoding a protein homologous with one subunit of an ATP-binding
cassette transporter. The cycA gene encodes a 17-residue
N-terminal signal peptide with following amino acid sequence identical
to that reported by (Titani, K., Ericsson, L. H., Hon-nami, K.,
and Miyazawa, T. (1985) Biochem. Biophys. Res. Commun. 128, 781-787). A modified cycA was placed under control of the
T7 promoter and expressed in Escherichia coli. Protein
identical to that predicted from the gene sequence was found in two
heme C-containing fractions. Fraction rC552,
characterized by an -band at 552 nm, contains ~60-70% of a
protein highly similar to native cytochrome
c552 and ~30-40% of a protein that contains
a modified heme. Cytochrome rC552 is monomeric
and is an excellent substrate for cytochrome ba3. Cytochrome rC557
is characterized by an -band at 557 nm, contains ~90% heme C and
~10% of non-C heme, exists primarily as a homodimer, and is
essentially inactive as a substrate for cytochrome
ba3. We suggest that
rC557 is a "conformational isomer" of
rC552 having non-native, axial ligands to the
heme iron and an "incorrect" protein fold that is stabilized by
homodimer formation.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 1998 by the American Society for Biochemistry and Molecular Biology.
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