Clarke Group
Biophysical chemistry of membranes and membrane proteins
We aim to increase understanding of the mechanism of ion transport across biological membranes and how it is influenced by the lipid surroundings. Malfunction of ion transporters leads to a multitude of diseases, particularly neurological diseases, and a massive effort is underway internationally in the development of drugs targeting transporters.
In our research, rather than directly developing new drugs, we aim to aid in their development by providing improved understanding of transporter mechanisms. Just like a mechanic fixing a broken car, our motto is that you have have to understand how something works before you try and fix it.
Our research focusses on both the protein and lipid components of biological membranes. With regards to the protein component, we have a longstanding interest in ion pumps, in particular P-type ATPases. A prime example is the Na+,K+-ATPase, which plays a vital role in controlling the volume of all animal cells, preventing them from shrinking or expanding and bursting. Other examples are the H+,K+-ATPase, which produces the acid environment in the stomach necessary for digestion, and the sarcoplasmic reticulum Ca2+-ATPase, which enables muscle relaxation.
Because all of these enzymes are embedded in a membrane, their activities are crucially dependent on the surrounding membrane’s composition, e.g. lipid saturation, chain length, cholesterol content. However, the means by which lipid-protein interactions modulate membrane function are still not fully understood. In our research we are focussing particularly on electrostatic interactions between membrane proteins and charged and dipolar groups of the surrounding lipids.
We are currently investigating the role of the N-terminus of P-type ATPases in regulation of their pumping activity. The N-terminus of several pumps are rich in positively charged lysine residues which may interact electrostatically with negatively charged lipids in the surrounding membrane. This could preferentially stabilise particular enzyme conformational states over others and provide a mechanism for ion pump regulation. If the details of this mechanism can be resolved, then it could potentially provide a target for the inhibition of the pumps of pathogenic bacteria.
Any drug molecule whose target is located within a cell must cross the barrier of the cell membrane. An important test applied by all pharmaceutical companies is to determine a new drug’s octanol/water partition coefficient as a measure of lipophilicity. The theory is that a drug which preferentially interacts with the nonpolar hydrocarbon tails of octanol is likely also to bind to a lipid membrane and diffuse across it. However, the structure of octanol bears little resemblance to a real lipid molecule. Using a recently developed instrument, the surface electrogenic event reader (SURFE2R), of which our lab possesses the only one in the Southern Hemisphere, we aim to screen drugs for interaction with real lipid membranes and determine the chemical properties of a drug molecule which promote membrane interaction and permeation.
For information about opportunities to work or collaborate with the Clarke group, please contact Associate Professor Ronald Clarke.
