The Tucker Lab - K⁺ Channel Research Group

Our research is focussed on understanding the intimate relationship between ion channel structure and function. The objectives are to understand how and why ion channels do what they do i.e. to understand their molecular mechanism of operation at an atomic level as well as understanding their role in physiology and disease.  As a model system we work primarily with the inwardly-rectifying family of potassium channels or ‘Kir’ channels as well as the K2P family of channels. The human genome contains fifteen different Kir channel genes divided into seven major subfamilies (Kir1.0-Kir7.0).  Like other potassium (K+) channels, Kir channels function as tetramers with each subunit contributing to the pore of the channel.  Each individual subunit has two transmembrane (TM) domains and large cytoplasmic domains which are involved in the response of Kir channels to factors such as G-proteins, PIP2, ATP and intracellular pH.  Kir channels are therefore able to regulate cellular electrical activity and K+ transport processes by coupling channel activity to a wide range of metabolic and physiological stimuli.  Their importance is illustrated by the fact that inherited mutations in Kir channels underlie Type II Bartter’s Syndrome (Kir1.1), Andersen’s Syndrome & Short QT Syndrome (Kir2.1), and certain forms of neonatal diabetes and hyperinsulinaemia (Kir6.2).

One of our main interests is the group of pH-sensitive Kir channels: Kir1.1 (KCNJ1), Kir4.1 (KCNJ10), Kir4.2 (KCNJ15) and Kir5.1 (KCNJ16). These channels have the ability to heteromultimerise and form novel channels which are exquisitely sensitive to inhibition by intracellular acidification. Our current projects include using a powerful combination of molecular biology, unnatural amino-acid mutagenesis, X-ray crystallography and electrophysiology (macroscopic and single-channel recording) to understand the molecular and structural basis of Kir channel gating (i.e. how they open and close), how they sense intracellular pH (i.e. H+), how different Kir channel subunits heteromultimerise with each other.  We have also previously investigated the role of Kir5.1 function in vivo using a Kir5.1 (Kcnj16) gene knockout model. Our lab is also very interested in the two-pore (K2P) family of potassium channels (TREK-1, TREK-2, TRESK) which are also pH-sensitive and have been investigating the structural basis of their gating mechanism.

Opening of bundle crossing gate in KirBac3.1 mutant channel

The other major focus of our laboratory is the use of prokaryotic K+ channel homologs as model systems to understand K+ channel structure and function. Many of these prokaryotic channels have extremely robust biophysical and biochemical properties which permits their analysis using a wide range analytical techniques not possible with mammalian K+ channels. Furthermore, such robust biochemical properties means that these membrane proteins also have the potential to be exploited as molecular devices. However, to realise this potential first requires a much better understanding of their fundamental biophysical properties such as gating, rectification and ionic selectivity.  Prokaryotic channels can also be used as pharmacological screens to identify agents which modulate K+ channel function.  Such tools would be of enormous use, not just as probes of K channel structure/function, but also as probes to dissect prokaryotic physiology where the role of many ion channels is still unknown.