Biological complexity: potassium ion channel controls (Introduction)

by David Turell , Thursday, June 21, 2018, 18:30 (2130 days ago) @ David Turell

Ions must be controlled as they cross cell membranes. This article describes potassium control by a special amino acid and how to reverse it:

https://phys.org/news/2018-06-team-reverse-potassium-channels-bacteria.html

"For the first time ever, researchers at the Texas Tech University Health Sciences Center (TTUHSC) have identified a specific amino acid residue that is responsible for inverting the communication between the opening of the activation gate and the inactivation of a potassium channel's selectivity filter.

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"'Normally, a potassium channel opens the activation gate and manages ion conduction for hundreds of milliseconds, then because the activation gate and the filter cross-talk, the filter undergoes a change in its conformation that yielded its collapse, which ceases ion conduction, inactivating the channel," Cuello said.

"Potassium channels are extremely specialized proteins that are embedded in a membrane that is surrounding any living cell. By closing and opening a narrow constriction known as the activation gate, they control the transport of potassium ions in and out of the cell. The selectivity filter of potassium channels is the region within the protein structure in charge of the selective discrimination between potassium and sodium ions, which are about the same size. Cuello said this area of the protein procures a passage that perfectly fits potassium ions but is incapable to accommodate sodium ions, which makes it "selective" for potassium ions. The filter also can act as a secondary gate in series to the activation gate.

"'The opening of the activation gate induces the collapsing of the selectivity filter which preclude the flow of ions through it despite having the activation gate open. The collapsing of a potassium channel is the underlying cause for a process known as C-type inactivation, which makes the selectivity filter the C-type inactivation gate."

"Potassium channels are proteins that are made of amino acid residues. A THREONINE is one of the 20 different amino acid residues that a cell uses to build a protein molecule. Cuello's lab identified a Threonine residue (Threonine 75) as a crucial player that communicates the opening of the activation to the channel selectivity filter.

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"Cuello's research found a way to reverse this process in a mutant channel, the threonine to alanine mutation in channels from bacteria all the way up to humans reverts the process. These mutant channels have a selectivity inactive filter when the activation gate is closed and resets to a conductive conformation when the activation gate is open."

Comment: this lab work found a specific amino acid change by design. It had to develop in nature by design. In fact the whole channel is so complex, it had to be designed.