Scientists are now able to "see" a structure that acts as an atomic-size sorter for cells. Without it, many important life functionsnerve signal firing, heartbeat, hormone secretioncould not occur.
The "selectivity filter," never before visualized in such exquisite detail, provides precise biochemical conditions needed for ions during their intercellular travel.
Ions, the electrically charged atoms that power many vital functions, traverse cell membranes through specialized proteins called ion channels. The proteins provide pathways between the inner part of the cell and the exterior. The selectivity filter is the essential part of the pathway.
The three-dimensional image of the selectivity filter, revealed by X-ray crystallography, is the culmination of several years work by Rockefeller University researchers from the Laboratory of Molecular Neurobiology and Biophysics. Professor and Howard Hughes Medical Institute Investigator Roderick MacKinnon, M.D., who heads the lab, and his colleagues describe their work in the Nov. 1 issue of Nature.
The image shows the selectivity filter of the channel that only the potassium ion can use to cross the cell membrane. In the same issue of Nature, MacKinnon and his colleagues report in another paper how the filter changes its shape under different environmental conditions within the body.
"We know the overall channel structure will be similar in channels that conduct potassium, sodium and calcium ions, but the chemistry in the selectivity filter will be unique in each specific case," says MacKinnon.
The selectivity filter also occupies a unique place in the potassium ion channel. The overall protein consists of four subunits, like four staves of a barrel. Inside the protein is a narrower tube called the selectivity filter where the potassium ion is recognized by the
Contact: Lynn Love