Experiments at UC Irvine (Luecke Lab), UCLA (Sachs Lab)
and the U.S. Department of Energy’s (DOE) SLAC National
Accelerator Laboratory have revealed a potential new way to attack
Helicobacter pylori (H. pylori) bacteria, via disrupting their own
mechanism for protecting themselves against gastric acid. The
breakthrough was achieved using powerful X-rays from SLAC’s
Stanford Synchrotron Radiation Lightsource (SSRL), by which
the three-dimensional molecular structure of this promising drug
target has been deciphered.
On the Cover of this issue of Immuno-Gastroenterology, we
present a diagram showing the first-ever glimpse of the six-molecule
ring of acid-gated urea channels embedded in the membrane of
H. pylori bacterium. Solving the structure of the protein to find
the specific area to target was rather demanding. The channels are
formed by the protein embedded in the bacterium’s cell membrane,
and membrane proteins are notoriously difficult to crystallize,
which is a prerequisite for using protein crystallography, the main
technique for determining protein structures. This technique
bounces X-rays off the electrons in the crystallized protein to
generate the experimental data used to build a 3-D map showing
how the protein’s atoms are arranged.
The six-molecule ring of urea channels is embedded in the
plasma membrane of H. pylori. When the periplasmic pH is below
6, urea passes from the gastric juice through the center of each of
the six channel molecules to the cytoplasm, where cytoplasmic
urease hydrolyzes it into ammonia and carbon dioxide, which in
turn buffer the periplasm. The center of the ring is filled with a
lipid bilayer plug. Blocking this channel with a drug would disable
this protective system, leading to a new and specific treatment for
people with the infection, without the side effects of broadband
antibiotics, and possibly with lower failure rates due to resistance,
approaching 30% for the current triple-therapy regimen.