Specific inhibition of the translocation of a subset of XXXX TAT substrates by the TorA signal peptide.

@entity6633 @entity1507 @entity3733 @entity369 @entity5189 @entity526
The SufI protein and the @entity6633 reductase (TorA) are the two best-characterized prototype proteins exported by the @entity526 TAT system. Whereas SufI does not contain cofactors, TorA is a molybdo-enzyme and the acquisition of the molybdo-cofactor is a prerequisite for its translocation. The overproduction of each protein leads to the saturation of its translocation, but it was unknown if the overproduction of one substrate could saturate the TAT apparatus and block thus the translocation of other TAT substrates. Here, we showed that the overproduction of SufI saturated only its own translocation, but had no effect of the translocation of TorA and other TAT substrate analyzed. To dissect the saturation mechanism of TorA translocation, we shortened by about one-third of the TorA protein and removed nine consensus molybdo-cofactor-binding ligands. Like SufI, the truncated TorA (TorA502) did not contain cofactor and would not compete with the full length TorA for molybdo-cofactor acquisition. The overproduction of TorA502 completely inhibited the export of the full length TorA and @entity3733 ( @entity3733 ) reductase, but had no effect on the translocation of SufI, @entity1507 -induced @entity5189 dehydrogenase and hydrogenase-2. Importantly, deletion of the twin- @entity369 signal peptide of TorA502 abolished the inhibitory effect. Moreover, the overproduction of the TorA signal peptide fused to the green fluorescence protein (GFP) was sufficient to block the TorA translocation. These results demonstrated that the twin- @entity369 signal peptide of the TorA protein specifically inhibits the translocation of a subset of TAT substrates, probably at the step of their targeting to the TAT apparatus.
