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Mapping membrane protein interactions on the molecular scale
with unnatural amino acids -- From the Mehl Research Lab at Franklin & Marshal
College
If we could zoom into the tip of a cell
we would see a myriad of complex proteins
interacting designed help the cell
communicate with the outside world. These
interacting membrane proteins in bacteria
communicate to the cell what chemicals
are outside and where to swim in a process
called chemotaxis. These systems in
bacteria are the models for how all cells
communicate in living organisms.
Unfortunately because these proteins are
stuck in the membrane they can not be
removed to be studied and we don’t know
how they are organized or move to perform
their complex signaling tasks. To test some
of the hypothetical structures shown here
we go into the living cell - into the proteins
with unnatural photoreactive amino acids.
Signal binds
Periplasm
Membrane
Cytoplasm
Change individual amino acids at the tip
O
Change F373
to photoreactive
amino acid
shine
light
on cells
and
separate
By placing these photoreactive amino acids at
Irradiation
defined location within the protein in the living
0
45
0
15
45
time (min)
cell we can map out how the proteins and when
Trimer crosslink
the proteins are contacting each other. If two
proteins are touching at the location of the
Dimer crosslink
photoreactive amino acid they form a permanent
bond. The covalently attached proteins can be
removed from the cell and investigated to
ascertain the organization of proteins in the
membrane. In this pictorial example we have
shown that the bacterial chemotactic receptor,
Tsr monomer
tsr, is organized as a trimer of dimers in its
functional form. Using this technology we can
Native Tsr
Tsr-373-pBpa
study the interactions of any protein in side the
living cell.
Ryan A. Mehl, Department of Chemistry, Franklin &Marshall College