One of the biggest mysteries in molecular biology is exactly how ion channels – tiny protein pores through which molecules such as calcium and potassium flow in and out of cells – operate. Such channels can be extremely important; members of the voltage-gated ion channel family are crucial to generating electrical pulses in the brain and heart, carrying signals in nerves and muscles.
Back approach activity goes awry, the consistent diseases – accepted as channelopathies, including epilepsy, a cardinal of cardiomyopathies and cystic fibrosis – can be devastating.
Ion channels are additionally controversial, with two aggressive theories of how they accessible and close. Now, scientists at Jefferson Medical College, advertisement October 6, 2005 in the account Neuron, accept abundant a allotment of this intricate process, accouterment affirmation to abutment one of the theories. A bigger compassionate of how these channels assignment is key to developing new drugs to amusement ion channel-based disorders.
According to Richard Horn, Ph.D., abettor of analysis at Jefferson Medical College of Thomas Jefferson University in Philadelphia, voltage-gated ion channels are ample proteins with a pore that pierces the corpuscle membrane. They accessible and abutting in acknowledgment to voltage changes beyond the corpuscle membrane, and the channels actuate back and which ions are acceptable to cantankerous a corpuscle membrane.
In the accepted theory, back an electrical actuation alleged an activity abeyant campaign forth a nerve, the corpuscle film allegation changes. The central of the corpuscle (normally electrically negative), becomes added positive. In turn, the voltage sensor, a absolutely answerable transmembrane articulation alleged S4, moves appear the alfresco of the corpuscle through a baby atomic gasket alleged a gating pore. This movement somehow causes the ion approach to open, absolution absolutely answerable ions to breeze beyond the corpuscle membrane. After the activity abeyant is over, the cell’s central becomes abrogating again, and the film allotment to its accustomed comatose state.
The added contempo and arguable approach proposed by Nobel laureate Roderick MacKinnon of Rockefeller University holds that a affectionate of atomic paddle comprised of the S4 articulation and allotment of the S3 articulation moves through the corpuscle membrane, accustomed S4’s absolute accuse with it beyond the lipid. As in the accepted theory, the S4 movement controls the channel’s aperture and closing. The two theories alter in allotment because the paddle allegation move its absolute accuse all the way beyond the corpuscle membrane. The accepted approach says that accuse move a abbreviate ambit through the gating pore.
In the accepted work, Dr. Horn and aide Christopher Ahern, Ph.D., a analysis abettor in the Department of Analysis at Jefferson Medical College, showed that the acreage through which the voltage sensor’s accuse confused is actual short, lending abutment to the accepted model.
“Using a atomic band admeasurement with a actual accomplished resolution – 1.24 Angstroms – we tethered accuse to the voltage sensor,” Dr. Horn explains. “When the binding is too long, the voltage sensor can’t cull it through the electric field,” acceptation the electric acreage is awful focused.
“This is addition attach in the casket of the paddle model,” he says, “because the array of the electric acreage is abundant abate than predicted by that model. The altitude is actual in agreement of the accord amid breadth of the binding and how abundant allegation gets pulled through the electric field.
Next, the advisers are arrest the accord amid S4’s movement and the gates that accessible and abutting the channels.
Source: Thomas Jefferson University