| Abstrakt: |
The conversion to mucoid phenotype in Pseudomonas aeruginosa during chronic infections in cystic fibrosis (CF) is due to mutations in the algU mucABCD gene cluster. This cluster encodes an extreme stress response system conserved in Gram-negative bacteria. The system includes an ECF sigma factor, AlgU (δ[sup E]), an inner membrane protein, MucA, which inhibits AlgU activity, and MucB, a periplasmic protein that negatively controls AlgU. In this work, we investigated whether and how these factor interact to transduce signals between different cellular compartments. The mutation mucAΔG440, which renders a large fraction of P. aeruginosa CF isolates mucoid, did not abrogate AlgU-MucA interactions, although it eliminated MucA-MucB interactions in the yeast two-hybrid system. The mucAΔG440 truncation of the periplasmic C-terminal tail of MucA destabilized the molecule resulting in low or undetectable steadystate levels in P. aeruginosa. Somewhat reduced levels of MucA were also seen in cells with inactivated mucB or with the mucACF53 allele carrying the missense P184S mutation, which mildly affected interactions with MucB. The events downstream from MucA destabilization were also investigated. AlgU was found to associate with inner membranes in mucA[sup +] cells. In mutants destabilizing MucA, a limited redistribution of AlgU from the membrane to the cytosol was observed. The redistribution was spontaneous in mucAΔG440 cells, while in mucB and mucACF53 mutants it required additional signals. Despite a large reduction in MucA levels in mucAΔG440 cells, only a small fraction of AlgU was redistributed to the cytosol and a significant portion of this δ factor remained membrane bound and behaved as a peripheral inner membrane protein. The fraction of AlgU that depended on MucA for association with the membrane also brought RNA polymerase into this compartment. These results are consistent with a model in which MucB-MucA-AlgU-RNA... [ABSTRACT FROM AUTHOR] |
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