This thesis will involve in vivo structural studies of membrane-bound receptors which have been linked to HIV infection, Parkinson's disease and schizophrenia. These receptors are members of a class of receptors involved in intracellular singalling, known as G protein coupled receptors (GPCR). Viruses, such as HIV exploit these receptors to gain entry into cells and cause disease. It is currently unknown how these large viruses interact with the receptors, and with what stoichiometry. We propose to study this interaction by a recently developed method (DEER, for Double Electron Electron Resonance). This technique efficiently measures long distances between two labels, and can thus be used to determine the distance between two GPCRs during interaction with a viral capsid. This project is a collaboration between a physico-chemical laboratory for the distance measurements, several biological research teams for the cellular models and a biotechnology company for the labelling system.