Unraveling the Structural Organization of Potassium Uptake System KtrAB

Abstract

Potassium ion flux across cellular membranes is mediated by a variety of protein channels and transporters. While ion channels provide pores through which select ions move down their electrical or chemical gradients at very high flux rates, ion transporters, on the other hand, show saturation for their substrates and may drive ions up their electrochemical gradient. Together, ion channels and transporters are critical components in the maintenance of cellular homeostasis, including osmolarity and pH as well as in electrical impulse propagation in higher organisms. We have previously demonstrated the RCK-domain octameric ring conformation for KtrAB potassium transporter. We focused on further characterizing this structural organization, obtaining high resolution atomic details by X-ray crystallography. We have therefore optimized overproduction and purification of full-length cytoplasmic (KtrA) and membranar (KtrB) components as well as the complex assembly. Ultimately, structural details will help understand conduction and regulation of potassium ion transport in KtrAB.