Pathogenic mycobacteria resist lysosomal delivery after uptake into macrophages, allowing them to survive intracellularly. We found that the eukaryotic-like serine/threonine protein kinase G from pathogenic mycobacteria was secreted within macrophage phagosomes, inhibiting phagosome-lysosome fusion and mediating intracellular survival of mycobacteria. Inactivation of protein kinase G by gene disruption or chemical inhibition resulted in lysosomal localization and mycobacterial cell death in infected macrophages. Besides identifying a target for the control of mycobacterial infections, these findings suggest that pathogenic mycobacteria have evolved eukaryotic-like signal transduction mechanisms capable of modulating host cell trafficking pathways.
This study is the first to show the immunoregulatory effect of VIP in humans, and supports the notion of inhaled VIP as an attractive future therapy to dampen exaggerated immune responses in lung disorders. Thus, the inhalation of neuropeptides may be developed into a new therapeutic principle for chronic inflammatory lung disorders in humans.
The signal-recognition particle (SRP) is important for the targeting of many secretory and membrane proteins to the endoplasmic reticulum (ER). Targeting is regulated by three GTPases, the 54K subunit of SRP (SRP54), and the alpha- and beta-subunits of the SRP receptor. When a signal sequence emerges from the ribosome, SRP interacts with it and targets the resulting complex to the ER membrane by binding to the SRP receptor. Subsequently, SRP releases the signal sequence into the translocation channel. Here we use a complex of a ribosome with a nascent peptide chain, the SRP and its receptor, to investigate GTP binding to SRP54, and GTP hydrolysis. Our findings indicate that a ribosomal component promotes GTP binding to the SRP54 subunit of SRP. GTP-bound SRP54 is essential for high-affinity interaction between SRP and its receptor in the ER membrane. This interaction induces the release of the signal sequence from SRP, the insertion of the nascent polypeptide chain into the translocation channel, and GTP hydrolysis. The contribution of the ribosome had previously escaped detection because only synthetic signal peptides were used in the analysis.
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