Accumulation of a mixed disulfide between DsbA and DsbB in
dsbB R48 mutants under aerobic conditions. Proteins of
cells growing exponentially in M63 medium were AMS-alkylated, separated
by native SDS/PAGE, and subjected to Western blotting with anti-DsbA
serum (lanes 1–8) or purified DsbB antibody (lanes 9–16). HK205 (wild
type; lanes 1, 7, 9, and 15), HK207 (dsbB C41Y; lanes 2
and 10), HK209 (dsbB R48C; lanes 3 and 11), HK211
(dsbB R48H; lanes 4 and 12), HK227
(dsbB∷Kan; lanes 5, 8, 13, and 16), and HK229
(dsbA∷Kan; lanes 6 and 14). Cells contain plasmid
pHP18 carrying dsbA C33Y in lanes 7, 8, 15, and 16. ∗,
DsbA–DsbB complex; oxi, the oxidized form of DsbA; red, the reduced
form of DsbA; arrowhead, DsbA C33Y; arrows, a nonspecific crossreacting
band. Positions of molecular mass standards are indicated on the left.
The migration of mixed-disulfide complexes differs slightly reflecting
differences in the number of free cysteine residues in each complex:
DsbA–DsbBR48C (+1), DsbA–DsbBR48H (0), DsbAC33Y–DsbB (−1).