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J Bacteriol, May 1998, p. 2694-2700, Vol. 180, No. 10
Department of Biochemistry, University of
Connecticut Health Center, Farmington, Connecticut 06030
Received 29 December 1997/Accepted 16 March 1998
Methionine residues in
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
In Vitro and In Vivo Oxidation of Methionine
Residues in Small, Acid-Soluble Spore Proteins from
Bacillus Species

/
-type small, acid-soluble spore
proteins (SASP) of Bacillus species were readily oxidized
to methionine sulfoxide in vitro by t-butyl hydroperoxide
(tBHP) or hydrogen peroxide (H2O2). These
oxidized
/
-type SASP no longer bound to DNA effectively, but DNA
binding protected
/
-type SASP against methionine oxidation by
peroxides in vitro. Incubation of an oxidized
/
-type SASP with
peptidyl methionine sulfoxide reductase (MsrA), which can reduce
methionine sulfoxide residues back to methionine, restored the
/
-type SASP's ability to bind to DNA. Both tBHP and
H2O2 caused some oxidation of the two
methionine residues of an
/
-type SASP (SspC) in spores of
Bacillus subtilis, although one methionine which is highly
conserved in
/
-type SASP was only oxidized to a small degree.
However, much more methionine sulfoxide was generated by peroxide
treatment of spores carrying a mutant form of SspC which has a lower
affinity for DNA. MsrA activity was present in wild-type B. subtilis spores. However, msrA mutant spores were no
more sensitive to H2O2 than were wild-type spores. The major mechanism operating for dealing with oxidative damage
to
/
-type SASP in spores is DNA binding, which protects the
protein's methionine residues from oxidation both in vitro and in
vivo. This may be important in vivo since
/
-type SASP containing
oxidized methionine residues no longer bind DNA well and
/
-type
SASP-DNA binding is essential for long-term spore survival.
*
Corresponding author. Mailing address: Department of
Biochemistry, University of Connecticut Health Center, Farmington, CT 06030. Phone: (860) 679-2607. Fax: (860) 679-3408. E-mail:
setlow{at}sun.uchc.edu.
Present address: Escuela de Ciencias Quimico Biologicas,
Universidad Autonoma de Guerrero, Chilpancingo, Guerrero 39000, Mexico.
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