A technique to label proteins that the pathogen Salmonella enterica injects into host cells is published online this week in Nature Methods. This will shed light on the function of these proteins and point to ways in which Salmonella infection may be prevented. Knowing exactly when and where pathogens use their proteins will be important information in conquering them.
Salmonella are pathogens that cause severe gastroenteritis and typhoid fever in humans. This bacterial pathogen enters the host cell by first injecting some of its proteins into the host which then allow the whole bacterium to gain entry into the host. Once inside, a second wave of bacterial proteins is injected into the interior of the host cell, aiding in the proliferation of the bacteria. The timing and location of the second wave of proteins is tightly regulated by the bacteria.
To follow these proteins Amy Palmer and colleagues tagged them with part of a fluorescent protein that only starts to glow when it is complemented with the other part of the same fluorescent protein that is expressed in the host cells. This protein complementation assay allows the researchers to follow several Salmonella proteins after injection into the live host cell and to visualize how they co-opt the cellular machinery for their own purposes.