หน้าหลัก

9). In the lptO mutant, PG0026 is absent from the membrane and is found instead accumulated in the periplasm (Figs. 5 and 6) (33). This means that both LptO and PG0026 are not functioning in the lptO mutant, but because the defect in gingipain secretion and maturation is total in the lptO mutant, LptO must be essential for gingipain secretion, whereas PG0026 is not. Furthermore, mutation of PG0026 had no effect on the deacylation of lipid A, whereas LptO was found to be essential for lipid A deacylation (33), indicating that LptO is still functioning in the PG0026 mutant in this respect. Partial CTD protein secretion in the PG0026 mutants is consistent with PG0026 functioning downstream of secretion. We therefore conclude that PG0026 cleaves the CTD after secretion of the CTD protein (Fig. 9). After secretion of PG0026 through the secretion pore by the same mechanism as other CTD proteins, PG0026 may be anchored on the cell surface via an interaction with LPS or an outer membrane protein. It is interesting in this regard that LptO was found exclusively in the OM fraction of the WT and PG0026 strains; however, in both PG0026 and PG0026C690A mutants, some LptO was also detected in the soluble fraction. Hence this may suggest that the efficient incorporation of LptO into the OM may be dependent on the presence of PG0026, and may imply an interaction between PG0026 and LptO at the cell surface. Alternatively, this observation could be due to the up-regulation in expression of LptO in both PG0026 and PG0026C690A mutants causing a concomitant overload to the normal kinetics of membrane insertion; however, this latter explanation is unlikely as LptO was also up-regulated in the PG0026 complementation strain but did not show any LptO in the soluble fraction (Fig. 6). After CTD cleavage by PG0026, the cleaved CTD dissociates, and A-LPS is conjugated to the new C terminus of the substrate protein, thereby anchoring the mature protein to the cell surface (Fig. 9). The conjugation may be performed by an uncharacterized domain of PG0026 such as domain A or B (Fig. 1A) or by an ancillary component of the PorSS. Other potential functions for domain A and B of PG0026 include cell surface binding and CTD cleavage selectivity. In conclusion, we propose that the major secretion pathway operating in the Bacteroidetes/Chlorobi phyla involves two https://britishrestaurantawards.org/members/neck40layer/activity/353350/ signals present in the secretory proteins. The first is an N-terminal signal peptide that directs translocation across the cytoplasmic membrane via the SEC machinery and is then cleaved by signal peptidase I. The second is the CTD signal that directs secretion across the OM via the PorSS machinery and is then cleaved by PG0026 prior to conjugation to A-LPS and surface attachment. To our knowledge, this is the first signal peptidase of Gramnegative bacterial secretion systems shown to cleave a C-terminally located signal. Author's ChoiceTHE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 288, NO. 34, pp. 24753?4763, August 23, 2013 ?2013 by The American Society for Biochemistry and Molecular Biology, Inc. Published in the U.S.A.Hepatitis C Virus NS5A Inhibits Mixed Lineage Kinase 3 to Block Apoptosis*Received for publication, June 6, 2013, and in revised form, July 12, 2013 Published, JBC Papers in Press, July 15, 2013, DOI 10.1074/j.