Differential thiol trapping of CadC in vivo The thiol/disulfide state of the periplasmic cysteines of CadC was monitored in vivo by differential thiol trapping according to [16]. The procedure was modified as follows: E. coli BL21(DE3)pLysS carrying one of the plasmids pET-CadC-C172A, pET-CadC-C172A,C208A or pET-CadC-C172A,C208A,C272A

was grown in phosphate buffered minimal medium with a pH of 7.6 or 5.8 to an OD600 of 0.5. Subsequently, overproduction of the CadC derivatives was induced by addition of 0.5 mM IPTG. After an additional hour of growth at 37°C, the OD600 was adjusted to 1, and 5 mM iodoacetamide (dissolved in 0.1 M Tris) was added to 1 ml cell suspension. At pH 7.6, incubation was performed for 15 min (37°C),

at pH 5.8 the incubation time was prolonged to 150 min to compensate the lower alkylation rate of iodoacetamide at low pH. www.selleckchem.com/products/bay-1895344.html This first alkylation procedure irreversibly modified all free thiol groups directly in the living cells. Subsequently, cells were harvested into 100 μl ice-cold 100% (w/v) trichloric acid (TCA) and stored on ice for at least 30 min. The TCA treated cells were centrifuged (16.000 g, 4°C, 15 min), and the resulting pellet was washed with 200 μl of ice-cold 10% (w/v) TCA followed PF-02341066 purchase by a wash with 100 μl of ice-cold 5% (w/v) TCA. The supernatant was removed completely, and the pellet was resuspended in 100 μl of denaturing buffer [6 M urea, 200 mM Tris-HCl (pH 8.5), 10 mM EDTA, 0.5% (w/v) SDS] supplemented with 10 mM DTT to reduce disulfide bonds. After one hour of incubation in the dark (37°C, gentle agitation at 1300 rpm), 10 μl ice-cold 100% (w/v) TCA was added, and the sample was stored on ice for at least

Olopatadine 30 min. After centrifugation, the resulting pellet was again washed with 200 μl of ice-cold 10% (w/v) TCA followed by a wash with 100 μl of ice-cold 5% (w/v) TCA. MM-102 chemical structure Finally, the pellet was resuspended in 50 μl of denaturing buffer containing 10 mM PEG-maleimide (Iris Biotech GmbH, Marktredwitz/Germany) to alkylate all newly reduced cysteines. The reaction (37°C, gentle agitation at 1300 rpm, in the dark) was stopped after one hour by addition of 5 μl ice-cold 100% (w/v) TCA. After precipitation on ice (30 min) and centrifugation, the pellet was washed first with 100 μl of 10% and then with 50 μl of 5% ice-cold (w/v) TCA. After removing the TCA, the pellet was washed twice with 500 μl acetone and resuspended in 50 μl denaturing buffer. Samples were mixed with non-reducing SDS-sample buffer and loaded onto 12.5% SDS-polyacrylamide gels [42]. CadC was detected by Western blot analysis [11]. Analysis of intermolecular disulfide bonds For the detection of intermolecular disulfide bonds, wild-type CadC and all available CadC derivatives with Cys replacements (CadC_C172A; CadC_C208A; CadC_C272A; CadC_C172A,C208A; CadC_C172A,C272A; CadC_C208A,C272A; CadC_C172A,C208A,C272A) were overproduced in E.