Journal of Bacteriology, April 2000, p. 2277-2284, Vol. 182, No. 8
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Received 22 September 1999/Accepted 22 January 2000
Rhodaneses catalyze the transfer of the sulfane sulfur from
thiosulfate or thiosulfonates to thiophilic acceptors such as cyanide and dithiols. In this work, we define for the first time the
gene, and hence the amino acid sequence, of a 12-kDa rhodanese from
Escherichia coli. Well-characterized rhodaneses are
comprised of two structurally similar ca. 15-kDa domains. Hence, it is
thought that duplication of an ancestral rhodanese gene gave rise to
the genes that encode the two-domain rhodaneses. The glpE
gene, a member of the sn-glycerol 3-phosphate
(glp) regulon of E. coli, encodes the 12-kDa
rhodanese. As for other characterized rhodaneses, kinetic
analysis revealed that catalysis by purified GlpE occurs by way of an
enzyme-sulfur intermediate utilizing a double-displacement mechanism requiring an active-site cysteine. The
Kms for SSO32
and
CN
were 78 and 17 mM, respectively. The apparent
molecular mass of GlpE under nondenaturing conditions was 22.5 kDa,
indicating that GlpE functions as a dimer. GlpE exhibited a
kcat of 230 s
1. Thioredoxin 1 from E. coli, a small multifunctional dithiol protein,
served as a sulfur acceptor substrate for GlpE with an apparent
Km of 34 µM when thiosulfate was near its
Km, suggesting that thioredoxin 1 or related
dithiol proteins could be physiological substrates for
sulfurtransferases. The overall degree of amino acid sequence identity
between GlpE and the active-site domain of mammalian rhodaneses is
limited (~17%). This work is significant because it begins to reveal
the variation in amino acid sequences present in the
sulfurtransferases. GlpE is the first among the 41 proteins in
COG0607 (rhodanese-related sulfurtransferases) of the database Clusters
of Orthologous Groups of proteins
(http://www.ncbi.nlm.nih.gov/COG/) for which sulfurtransferase activity
has been confirmed.
Present address: Department of Horticultural Science, North
Carolina State University, Raleigh, NC 27695-7609.
Present address: National Cancer Institute/Surgery Branch,
National Institutes of Health, Bethesda, MD 20892.
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