H. pylori and PaCS Figure 5. Proteasome is the particle component of PaCS which also contains NOD1. Selective PaCS reactivity for NOD1 (A, 12,500x; boxed part enlarged in its inset, 60,000x); ubiquitin-activating enzyme E1 (B, 10,000x; enlarged in its inset, 32,000x); 20S proteasome (C, 12,500x; enlarged in its inset, 60,000x); 20S-b5i subunit of immunoproteasome (D, 12,500x; enlarged in its inset, 60,000x); and 19S proteasome (E, 12,500x; enlarged in its inset, 60,000x). Note in F (10,000x) and its inset (32,000x) lack of immunogold particles in a PaCS and surrounding cytoplasm of a control section from the same resin block (as in A, B, and C) incubated with gold-labelled non-immune globulins. In G (125,000x), H (340,000x) and I (340,000x) high- resolution TEM of the 13-nm-thick PaCS particles, selectively immunoreactive for 19S proteasome (G), shows their inner punctate substructure with minute electrondense spots aligned perpendicularly to particle long axis. On a side view like that further enlarged in the inset of H (600,000x), some particles closely resemble the four parallel rings of a proteasome 20S core capped at both estremities, while on a top view like that in the inset of I (600,000x) they may reproduce the proteasome seven-fold star-like symmetry. n, nucleous. doi:10.1371/journal.pone.0009716.g005 ‘‘capped’’ proteasome, respectively, where the 20S core particle is extended at one or both extremities by the addition of the 19S or the PA28 ‘‘cap’’ [25–27]. The four-ring substructure of the 20S core proteasome was also recognized in some side views of the PaCS particle, with (Figure 5H and its inset) or without addition of cap structures at its extremities. In addition, ‘‘top’’ views of favorably oriented particles, so as to provide a cross section of the barrel (Figure 5I and its inset), also showed the characteristic seven-star structural pattern reported for isolated proteasome complex [25]. Control immunogold tests with rabbit or mouse immunoglob- ulins gave negative results in PaCSs (Figure 5F), as did antibodies directed against ribosomal proteins, cathepsin D, S-100 protein or insulin and glucagon hormones. Selective PaCS reactivity was also found for some cytosolic proteins known to interact with CagA, as SHP2 tyrosine phosphatase (Figure 6B) which forms complexes in PLoS ONE | www.plosone.org 7 March 2010 | Volume 5 | Issue 3 | e9716