COMPUTATIONAL ANALYSIS OF G-PROTEIN COUPLED RECEPTOR SCREENING, DIMERIZATION, AND DESENSITIZATION

Abstract

Mechanistic models of G-protein coupled receptor (GPCR) signaling are used to gain insight into how changes in drug properties affect cellular response. Broadly, this work is divided in to three areas focusing on drug screening, desensitization, and receptor dimerization. First, ordinary differential equation models are used to examine biases in drug screening assays such as those used in drug discovery. It is shown that some screens should be innately biased against detecting inverse agonists and as such may miss pharmaceutically valuable drug leads. However, the results also suggest ways in which the screening assay can be modified to correct this bias. Second, Monte Carlo simulations of protein diffusion and reaction are used to determine the effects of drug properties on GPCR activation and desensitization. For most GPCRs, drugs cause an initial burst of activity (activation) followed by an attenuation of the signal over long times (desensitization). Simulations of this activation and desensitization process show that the mean drug-receptor lifetime can affect desensitization in a way that allows receptor activation and desensitization to be partially decoupled. Third, Monte Carlo simulations of receptor dimerization and diffusion are used to show how dimerization can affect membrane organization. Many membrane bound proteins, including GPCRs, form transient dimers, but the physiological reason for dimerization is not clear. The simulations show that dimerization under diffusion limited conditions can lead to the formation of extended clusters. These clusters, in turn, can alter the receptor internalization rate and the degree of cross-talk among receptors, in agreement with experimental findings. Overall, this work has a variety of implications. Pharmacologically, this work presents a new way of making drug discovery a more rational process by focusing assays toward drugs with desirable efficacies and improved desensitization profiles. Similarly, receptor dimerization could also provide a novel mechanism for affecting drug signaling. For basic biology, the modeling work presented here suggests that dimerization could provide a new way to control protein organization within the cell membrane. Together this work helps us to provide us with a more mechanistic understanding of how cells communicate via GPCRs.