Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

29-POS Board 29 The Evolution of the Fast Inactivation Phase in Calcium-selective TRP Channels Lisandra Flores Aldama 1,2 , Daniel Bustos 3 , Juan Opazo 1 , Sebastian Brauchi 1,2 . 3 Universidad de Talca, Talca, Chile. 1 Universidad Austral de Chile, Valdivia, Chile, 2 CISNE, Valdivia, Chile, TRPV5 and TRPV6 are highly calcium-selective channels belonging to the Transient Receptor Potential (TRP) family. Both channels are considered as key elements in transcellular calcium transport, therefore, essential in the regulation of systemic calcium homeostasis. It was reported that intracellular calcium (Ca 2+ ) exerts a negative control over the activity of these channels. In this context, the observed channel inactivation has been divided in a fast and a slow phase. The latter depends on the binding of Ca 2+ -Calmodulin complex to the C-terminal of the channel, and it is common between both channels. In contrast, the fast inactivation phase depends on Ca 2+ ions alone and allows to differentiate both channels from a functional point of view. While TRPV6 shows a faster calcium-dependent inactivation, TRPV5 barely inactivates. It has been described that the intracellular loop S2-S3 and residues downstream the transmembrane segment S6 are involved in the differences seen in the kinetics of this fast inactivation, and therefore assumed part of this mechanism. Currently, the exact location of the putative calcium binding site and the molecular mechanism governing this process are not known. The present work propose a structural-functional model for this process. By means of phylogenetic reconstructions, molecular dynamics simulations, site-directed mutagenesis, and patch clamp electrophysiology, we have identified a binding site that put together three different portions of the folded channel, and show that subtle evolutionary-related variations within the binding region account for the differences seen in the fast inactivation phase.

75