In
E. coli bacterium, the inner membrane sensor protein CusS mobilizes from a
clustered form upon sensing copper ions in the environment. CusS recruits the
transcription regulator protein CusR and then breaks down ATP to phosphorylate
CusR, which then proceeds to activate gene expression to help the cell defend
against the toxic copper ions.
Cornell
researchers combined genetic engineering, single-molecule tracking and protein
quantitation to get a closer look at this mechanism and understand how it
functions. The knowledge could lead to the development of more effective
antibacterial treatments.
The bacteria's resistance
is actually a tag-team operation, with two proteins working together
inside the cell. One protein (CusS), in the inner membrane, senses the presence
of the chemical or metal and sends a signal to a regulator protein (CusR) in
the cytosol, or intercellular fluid. The regulator protein binds to DNA and
activates a gene that generates transport proteins, which purge the toxin from
the cell.
Microbiologists
analyze these functions by using biochemical assays that remove the protein
from the cell. However, that process prevents the scientists from observing the
proteins in their native environment, and certain details, such as the spatial
arrangement between proteins, have remained murky.
For
a deeper analysis, researchers used single-cell imaging, whereby they tagged
individual proteins in living E. coli with a fluorescent signal and imaged the
proteins one at a time, tracking their motions. The procedure yielded millions
of images and, ultimately, a finely detailed, qualitative map of the proteins' movement.
See:
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)
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