Analysis of surface exposure of P. gingivalis HmuY protein. (A) Proteinase K (PK) accessibility assay performed with whole-cell P. gingivalis wild-type A7436 and W83 strains and the hmuY deletion mutant (TO4) grown in basal medium supplemented with dipyridyl and with the purified protein (HmuY). The cells or protein were incubated with proteinase K at 37°C for 30 min and then analyzed by SDS-PAGE and Western blotting. Intact HmuY exposed on the cell surface was analyzed by dot-blotting (B) or FACS (C) analyses. For dot-blotting analysis, varying dilutions of P. gingivalis cell suspension (starting at OD660 = 1.0; 1 μl) were adsorbed on nitrocellulose membrane and detected with pre-immune serum or purified pre-immune IgGs and immune anti-HmuY serum or purified immune anti-HmuY IgGs. For FACS, P. gingivalis cells were washed and, after blocking nonspecific binding sites, incubated with pre-immune (grey) or anti-HmuY immune serum (transparent). Representative data of the P. gingivalis A7436 strain are shown.