D. Missiakas et al., IDENTIFICATION AND CHARACTERIZATION OF A NEW DISULFIDE ISOMERASE-LIKEPROTEIN (DSBD) IN ESCHERICHIA-COLI, EMBO journal, 14(14), 1995, pp. 3415-3424
Previous studies have established that DsbA and DsbC, periplasmic prot
eins of Escherichia coli, are two key players involved in disulfide bo
nd formation, A search for extragenic mutations able to compensate for
the lack of dsbA function in vivo led us to the identification of a n
ew gene, designated dsbD, Lack of DsbD protein leads to some, but not
all, of the phenotypic defects observed with other dsb mutations, such
as hypersensitivity to dithiothreitol and to benzylpenicillin. In add
ition, unlike the rest of the dsb genes, dsbD is essential for bacteri
al growth at temperatures above 42 degrees C, Cloning of the wild-type
gene and sequencing and overexpression of the protein show that dsbD
is part of an operon and encodes an inner membrane protein, A 138 amin
o acid subdomain of the protein was purified and shown to possess an o
xido-reductase activity in vitro, Expressing this subdomain in the per
iplasmic space helped restore the phenotypic defects associated with a
dsbD null mutation, Interestingly, this domain shares 45% identity wi
th the portion of the eukaryotic protein disulfide isomerase carrying
the active site. We further show that in dsbD mutant bacteria the dith
iol active sites of DsbA and DsbC proteins are mostly oxidized, as com
pared with wild-type bacteria, Our results argue that DsbD generates a
reducing source in the periplasm, which is required for maintaining p
roper redox conditions, The finding that overexpression of DsbD leads
to a Dsb(-) phenotype, very similar to that exhibited by dsbA null mut
ants, is in good agreement with such a model.