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Thioredoxins [1,2,3,4] are small proteins of approximately one hundred amino-acid residues which participate in various redox reactions via the reversible
oxidation of an active center disulfide bond. They exist in either a reduced
form or an oxidized form where the two cysteine residues are linked in an
intramolecular disulfide bond. Thioredoxin is present in prokaryotes and
eukaryotes and the sequence around the redox-active disulfide bond is well
conserved. Bacteriophage T4 also encodes for a thioredoxin but its primary
structure is not homologous to bacterial, plant and vertebrate thioredoxins.
A number of eukaryotic proteins contain domains evolutionary related to
thioredoxin, most of them are protein disulfide isomerases (PDI). PDI (EC
126.96.36.199) [5,6,7] is an endoplasmic reticulum enzyme that catalyzes the
rearrangement of disulfide bonds in various proteins. The various forms of PDI
which are currently known are:
PDI major isozyme; a multifunctional protein that also function as the β
subunit of prolyl 4-hydroxylase (EC 188.8.131.52), as a component of
oligosaccharyl transferase (EC 184.108.40.206), as thyroxine deiodinase (EC 3.8.
1.4), as glutathione-insulin transhydrogenase (EC 220.127.116.11) and as a thyroid
hormone-binding protein !
ERp60 (ER-60; 58 Kd microsomal protein). ERp60 was originally thought to be
a phosphoinositide-specific phospholipase C isozyme and later to be a
All PDI contains two or three (ERp72) copies of the thioredoxin domain.
Bacterial proteins that act as thiol:disulfide interchange proteins that
allows disulfide bond formation in some periplasmic proteins also contain a
thioredoxin domain. These proteins are:
Escherichia coli dsbA (or prfA) and its orthologs in Vibrio cholerae (tcpG)
and Haemophilus influenzae (por).
Escherichia coli dsbC (or xpRA) and its orthologs in Erwinia chrysanthemi
and Haemophilus influenzae.
Escherichia coli dsbD (or dipZ) and its Haemophilus influenzae ortholog.
Escherichia coli dsbE (or ccmG) and orthologs in Haemophilus influenzae,
Rhodobacter capsulatus (helX), Rhiziobiacae (cycY and tlpA).
The pattern we developed is directed against the two cysteines that form the
redox-active bond. We also developed a profile that covers the whole domain.
December 2007 / Profile added and text revised.
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