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. The effects of cholesterol on these interactions is currently a major area of our interest.
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.
Conformational changes of membrane proteins which change their hydrophobic thickness must lead to deformations in the surrounding membrane. Thus the energetics of conformationally active membrane proteins must incorporate the energy cost of membrane bending. To determine quantitatively the energy changes involved we are carrying out calorimetric studies of membranes of defined compositions to determine the effects of cholesterol, oxidized cholesterol derivatives, lipid chain length and specific ions.
Dr Rufaka Hossain, Postdoctoral Research Fellow
Dil Diaz, MSc student
Caitlin MacKintosh, MChem student
Amy Gorman, MChem student
For information about opportunities to work or collaborate with the Clarke group, please contact Ron Clarke.