Studies on the Protein-assisted Mechanism for Intracellular Membrane Contact Sites

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This project will probe the mechanism of lipid movement between cellular compartments known as organelles. Recently, strong evidence indicates that most lipid transport occurs with the help of lipid transport proteins that can facilitate the formation of organelle contacts known as membrane contact sites. The oxysterol binding homologue (Osh) proteins of yeast are an example of lipid transport proteins that form membrane contact sites and serve as an excellent model for lipid exchange between organelles. Since cells can be used to produce chemicals for commercial use, understanding lipid exchange and ways to modify it could improve production of chemicals. This project will provide scientific training for researchers with focused recruitment from underrepresented groups. Project concepts and results will be used in educational outreach for minority-serving high school summer programs, courses, and developing hands-on protein engineering activities for the general public. Osh proteins were originally thought to transport sterols but have recently been shown to be important in the transport of signaling lipids, such as phosphatidylinositols. This project integrates experimental and computational techniques to elucidate membrane contact site formation and probe lipid exchange by first studying membrane-binding regions of Osh proteins and then the mechanism the full-length protein uses to form membrane contact sites. The binding of the lipid-packing sensor of Osh proteins to model membranes (planar and curved) will be probed using enhanced sampling simulations, neutron diffraction, and high-resolution field-cycling NMR. Other domains of Osh4 interacting with membranes will be studied with a focus on how this protein might conformationally change to facilitate membrane contact sites. Ultimately, the mechanism of the full-length Osh4 protein to form membrane contact sites and lipid transfer will be probed by developing new computational tools for dual-membrane binding and the use of field-cycling NMR and fluorescence techniques. This proposal is jointly funded by the Cellular Dynamics and Function cluster and Molecular Biophysics cluster in the Division of Molecular and Cellular Biosciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.