  In recent years, cell-based assays have been frequently used in molecular
interaction analysis. Cell-based assays complement traditional biochemical and
biophysical methods, as they allow for molecular interaction analysis, mode of
action studies and even drug screening processes to be performed under
physiologically relevant conditions. In most cellular assays, biomolecules are
usually labeled to achieve specificity. In order to overcome some of the
drawbacks associated with label-based assays, we have recently introduced
cell-based molography as a biosensor for the analysis of specific molecular
interactions involving native membrane receptors in living cells. Here, we
expand this assay to cytosolic protein-protein interactions. First, we created
a biomimetic membrane receptor by tethering one cytosolic interaction partner
to the plasma membrane. The artificial construct is then coherently arranged
into a two-dimensional pattern within the cytosol of living cells. Thanks to
the molographic sensor, the specific interactions between the coherently
arranged protein and its endogenous interaction partners become visible in
real-time without the use of a fluorescent label. This method turns out to be
an important extension of cell-based molography because it expands the range of
interactions that can be analyzed by molography to those in the cytosol of
living cells.
