Functional reconstitution of membrane proteins has been the major roadblock for the application of NMR and other biophysical techniques to investigate their high-resolution dynamic structures in a native membrane environment. In this application, we propose to develop approaches to enable high-resolution structural studies of membrane proteins and protein-protein complexes by a variety of biophysical techniques. We will develop nanodisc technology for detergent-free direct extraction and functional reconstitution of membrane proteins for structural studies of a variety of membrane proteins including single-pass transmembrane proteins (such as mammalian cytochromes and heme oxygenase) and integral membrane proteins (including GPCRs and Guanidine exporter). Synthetic polymers developed in our laboratory exhibit the ability to form nanodiscs with easily controllable sizes (from ~8 to ~60 nm diameter), are stable against pH and divalent metal ions and capable of directly extracting membrane proteins. Our preliminary results demonstrate that these nanodiscs (<20 nm diameter) and macro-nanodiscs (>20 nm diameter) represent an exciting system for solution and solid-state NMR studies of membrane proteins. We also propose to use the newly developed nanodisc technology and NMR approaches to investigate the structural interactions of mammalian cytochrome-P450 (P450) with its redox partners (P450-reductase (CPR) and cytochrome-b5 (b5)) to better understand how redox partners regulate P450 catalysis and how P450s metabolize chemically diverse substrates. The structural aspects pertaining to the catalytic activity of P450s continue to remain elusive due to a lack of high-resolution structures in their full-length, active forms. Presently, structural studies of P450s are restricted to various truncated mammalian and water-soluble bacterial P450 homologs. In this study, we will investigate the structure, dynamics and transmembrane domain orientation of full-length mammalian P450s (2B4, 3A4 and 3A5 isoforms) alone and in complex with its redox partner b5 and CPR, incorporated in nanodiscs, using a combination of high-resolution solution and solid-state NMR techniques. We will also investigate the ternary P450-b5-CPR complex in nanodiscs in the presence of substrates to elucidate the molecular origin of the strikingly different effects CPR and b5 have on P450 2B4 catalysis. The outcome of the proposed studies on P450-redox complexes will provide structure and dynamics/function principles regulating P450 metabolism of a wide variety of substrates. The results obtained from this study will also be useful to design potent drugs to ultimately treat and prevent diseases including cancer.
The proposed development of biophysical approaches to functionally reconstitute membrane proteins in near native lipid membrane would enable high-resolution structural studies to better understand their function. Human cytP450s are the target for the treatment of various diseases including prostate and breast cancer. The outcome of the proposed structural studies will provide powerful insights into the molecular mechanism by which P450 redox partners influence the catalytic activity of cytP450 that is responsible for the metabolism of more than 70% of the current-day pharmaceuticals.
