STRUCTURAL STUDIES OF ION CHANNELS

University Of Chicago, Chicago IL

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Ion channels are essential for living cells. There are about 80 different potassium channels classified into voltage-gated (Kv, 6TM),inward rectifying (Kir, 2TM), Calcium dependent (BK,6TM) and prokaryotic (KcsA,2TM). Voltage sensitive channels have a voltage sensor domain, transmembrane segments S1-S4, that responds to changes in membrane potential which triggers the pore domain to undergo the conformational change required to allow passage of ions. KcsA is a bacterial ligand gated potassium channel that opens on stimulus by intracellular protons. Generally the ion channel ?gating? refers to the conformational changes involved in the opening and closing of the conduction pathway. As for now, the crystal structure reveals only the closed state and the expectation is like most of the pore architecture remains intact in the open state. Shaker channel is a voltage gated K+ channel, composed of four subunits, each containing 6 transmembrane segments. An ion-pore module (S5-S6 equivalent to that of M1-M2 in KcsA) is surrounded by the voltage gating modules. So far the studies suggest that mutations in S4 segments affect channel gating, wherein, the S4 segments function as voltage sensors. In Shaker channel, the channel gate appears to be tightly coupled to the voltage sensors. KcsA has been successfully crystallized for numerous mutants and in various conditions. In contrast, the voltage-gated Shaker channel presents a more difficult challenge for crystallization. In this experiment our aim is to study the structural and functional aspects of Shaker by considering various KcsA-Shaker chimera. The hypothesis is that those chimera will be well behaved for crystallization, like KcsA. Expression and purification of the chimera were done and the crystallization screening is in progress.