Within the plasma membrane, the cytofacial and lumenal/exofacial leaflets of the bilayer are known to be composed of different phospholipid species. This unequal distribution of phospholipids within the bilayer is referred to as membrane phospholipid asymmetry. This asymmetry is coordinates a number of cellular functions ranging from membrane curvature, to secretory function, and intra- and intercellular signaling. Disruption of phospholipid asymmetry has been linked to neurological dysfunction, blood disorders, cholestasis, and type 2 diabetes. However, the means through which a cell maintains phospholipid asymmetry of the plasma membrane and internal organelles is poorly understood. One critical regulator of membrane phospholipid asymmetry is a family of enzymes called phospholipid flippases, or P4-type ATPases. My research plan will use forward genetic strategies and directed enzyme evolution to: i) determine the P4- ATPase residues used to discriminate phospholipid backbone, ii) define the molecular basis for phosphatidylethanolamine headgroup recognition, and iii) test the primary structural mechanism responsible for substrate protection and passage through the membrane. Elucidating these mechanisms will be critical to understanding how the cell sets, maintains, disrupts, and repairs phospholipid asymmetry of its membranes. These molecular findings will be critical for the design of new enzyme technologies for the perturbation and examination membrane asymmetry effectors within the nervous system, lymphocytes, vasculature, and hepatic system. Finally, we anticipate that a molecular understanding of substrate recognition and coordination will facilitate the production of pharmaceutical therapies for disease treatment.
The asymmetric distribution of phospholipids across the plasma membrane lipid bilayer coordinates a number of cellular functions in the nervous, immune, vascular, and hepatic systems; ranging from membrane curvature and secretory function, to intra- and intercellular signaling. The Type-4 class of P-Type ATPases, or phospholipid flippases, is a family of enzymes that govern this phospholipid asymmetry. This research project will elucidate the molecular mechanisms responsible for phospholipid substrate recognition and transport, and these findings will be critical to understanding how the cell sets, maintains, disrupts, and repairs phospholipid asymmetry of the membrane.
| Roland, Bartholomew P; Graham, Todd R (2016) Directed evolution of a sphingomyelin flippase reveals mechanism of substrate backbone discrimination by a P4-ATPase. Proc Natl Acad Sci U S A 113:E4460-6 |
| Roland, Bartholomew P; Graham, Todd R (2016) Decoding P4-ATPase substrate interactions. Crit Rev Biochem Mol Biol 51:513-527 |
