After washing, antibodies were eluted with 100 mM glycine pH 2.7. The pH of the eluent was immediately neutralized by the addition of 1/10 volume of 2 M Tris–HCl pH 8.0. The concentration of the antibodies in the eluent was estimated based on the absorption at OD280. Western blot hybridization

Proteins separated by SDS-PAGE were transferred onto ECL membrane (Amersham Bioscience) by semidry transfer and then incubated with 0.5 μg/ml purified antibodies against LytM185-316 protein. Goat anti-rabbit peroxidase-conjugated secondary antibodies (Sigma) were detected using Western Blot Luminol Reagent (Santa Cruz Biotechnology). LytM stability selleck products Supernatants from 1 ml cultures of S. aureus at late exponential phase were concentrated, mixed with 2 μg of LytM26-316, and incubated overnight at 37°C. Proteins were separated on SDS-PAGE and used for Western blot hybridization. selleck kinase inhibitor Selleck AZD2014 To assess the stability of lysostaphin and LytM185-316 in buffer with addition of blood or serum (from rat) enzyme was mixed with 5% or 50% blood or serum in 50 mM glycine pH 8.0, and incubated at 37°C. Protein samples were collected after 1 and 4 h, separated by SDS-PAGE and used for Western blot hybridization. Cell wall treatment Late exponential phase cultures of S. aureus grown in CASO Broth medium were harvested by centrifugation, resuspended in buffer A (20 mM Tris–HCl pH 7.5) and autoclaved for 20 min. Crude extract was obtained after sonicating

the cells for 3 min. The accessory wall polymers were removed by the following methods. SDS treated walls were boiled in 4% SDS for 30 min. Trypsinized walls were prepared by 8 h trypsin digest (0.5 mg/ml) at 37°C. Trichloroacetic acid (TCA) treatment was done by 48 h incubation in 10% TCA at 4°C. After each of these treatments, cell walls were extensively washed in buffer A. Purified peptidoglycans were prepared as described previously [12] by combining all methods described above. Alternatively, S. aureus peptigdoglycan was purchased

from Fluka Biochemika. Pulldown peptidoglycan binding Benzatropine assay To assess binding, 2 μg of protein was mixed with cell walls or peptidoglycans (100 μg) and incubated at room temperature for 15 min. Then, soluble and insoluble fractions were separated by centrifugation and peptidoglycans were washed with 1 ml of buffer A. Soluble fractions and washed peptidoglycans were mixed with loading buffer separated by SDS-PAGE and analyzed by Western blot hybridization. Final concentrations of 10 mM EDTA, 1 mM 1,10-phenanthroline, 10 mM N-acetylglucosamine, 10 mM glycine hydroxamate, 1 mM PMSF and 1 mM E-64 were used to test the influence of these compounds on peptidoglycan binding. Cell lysis assay S. aureus cells collected at the exponential growth phase were washed and suspended in buffer A supplemented with 200 μg/ml erythromycin. Then the cells were diluted to an apparent OD595 of 1.8 with an appropriate buffer.