Molecular mechanisms of lipid transfer by bridge-like lipid transfer proteins - Summary Cells and cellular organelles are surrounded by membranes that are constantly undergoing lipid modification due to processes like cell growth, organelle biogenesis, exocytosis, autophagy, phagocytosis, and temperature adaptation. The recently discovered, evolutionarily conserved superfamily of bridge-like lipid transfer proteins (BLTPs) are essential for all these processes due to their role in lipid transport. BLTPs localize to membrane contact sites, where they fold into hydrophobic tunnels that are proposed to function like “lipid superhighways” that mediate the bulk transfer of lipids from donor to acceptor membranes. Despite the fundamental importance of BLTPs in cellular function and organismal survival, little is known about how they function, largely due to challenges associated with producing of BLTPs in heterologous cell lines. The overarching goal of my research is to overcome these challenges and answer fundamental questions surrounding BLTP function, including (i) how do BLTPs transfer lipids from the donor to the acceptor membrane, (ii) what is the role of BLTP-mediated lipid transfer in cellular physiology, and (iii) how does BLTP dysfunction lead to disease. As a foundation for this work, we have recently elucidated the structure of a native BLTP complex from C. elegans, revealing unexpected structural and functional features that provide mechanistic insight into the process of lipid transfer. Over the next five years, our research will focus on understanding the molecular mechanisms of lipid transport by BLTP1 and BLTP2, two of the five members of the BLTP superfamily, using single particle cryo-electron microscopy in combination with complementary genetic, biochemical, and computational methods. We will address key outstanding questions in the field of BTLP-mediated lipid transfer, including the selectivity for specific membrane lipids, the regulation of transport, and the mechanisms of lipid extraction and delivery. Moreover, as mutations in BLTPs are implicated in multiple neurological disorders, we will harness the C. elegans and D. melanogaster model systems to investigate the molecular underpinnings of BLTP dysfunction in these diseases. The knowledge gained from this research will provide a comprehensive understanding of the relationships between BLTP structure and function that will illuminate the mechanisms of lipid transfer at membrane contact sites. In addition, the methods for native protein isolation and characterization that we develop over the course of this work can also be applied to other challenging protein complexes, enabling the study of clinically relevant, previously intractable proteins.
