Towards the molecular mechanism of solute carrier proteins

The results of various genome projects have shown that up to 30% of human proteins occur in cell membranes. The membrane transporters form the second largest family among these membrane proteins. The transporters are responsible for uptake and release of various substances including sugars, amino acids, drugs and minerals into or out of cells. Thus, membrane transporters play crucial roles in many biological functions and are of key importance for medicine and pharmacology. We need to understand membrane transporter structures to provide a basic understanding of life at the molecular level. Knowledge of the structure is also very useful for drug discovery enabling rational design of new small molecule ligands that can specifically inhibit the protein of interest and not affect other proteins, resulting in drugs with less side effects. This application is to study the structures and mechanisms of these transporters. To study the molecular properties of transporters, we use the method called ' protein X-ray crystallography'. For this method, it is essential to obtain crystals of the transporters, which are subsequently subjected to X-ray diffraction experiments. Although we have already obtained crystals of some transporters, it is still a difficult process to improve the crystals sufficiently to enable us to collect good quality X-ray diffraction data. This is because the membrane transporters are very hydrophobic and do not yield good quality crystals easily. Therefore, it would be extremely useful to perform this project at the new Research Complex at Harwell associated with Diamond Light Source. Good access to the high quality X-rays, produces by the beamlines at Diamond Light Source, are crucial for successful data collection from these membrane transporter crystals. The Diamond Light Source also accommodates the Diamond Membrane Protein Laboratory, a user facility for high throughput membrane protein crystallisation, which is also advantageous to facilitate optimisation of the crystals in this proposal.

The results of various genome projects have shown that up to 30% of human proteins occur in cell membranes. The membrane transporters form the second largest family among these membrane proteins and play crucial roles in many biological functions. Although a large amount of work has been done in biochemistry and molecular biology, very little is known about the molecular details and mechanisms of these transporters. The current classification of transporters and proposed molecular mechanisms could be totally re-written once a variety of transporter structures are solved. This project will focus on mammalian solute carriers or their orthologues. We have already obtained 13 diffracting crystals of these carrier proteins belong to 5 solute carrier families. These families are the facilitative GLUT transporter family (SLC2), the bicarbonate transporter family (SLC4), the sodium/proton exchanger family (SLC9), the sodium bile salt cotransport family (SLC10) and the proton oligopeptide cotransporter family (SLC15). We will determine the structures of these family transporters to reveal the detailed recognition mechanisms for a variety of molecules. We will combine structural biology, molecular biology and computer simulations to understand their molecular transport mechanisms. To achieve these objectives, it is essential to set up a new laboratory for transporter purification and characterisation in RCaH. Good access to synchrotron radiation facilities such as those at the Diamond Light Source (DLS) is one of the keys for successful determination of challenging protein structures. DLS is currently building a microfocus beamline optimal for data collection from weakly diffracting membrane protein crystals. DLS also accommodates the Membrane Protein Laboratory for high throughput membrane protein crystallisation, which is advantageous for optimising the crystals in this proposal.