How is bridge-like lipid transfer proteins (bltp) function regulated?

The National Institute of General Medical Sciences awarded the Regents Of The University Of Colorado, doing business as University Of Colorado-Denver, $429,000 on August 1, 2026, under the Biomedical Research and Research Training program (CFDA 93.859) to investigate the regulation of bridge-like lipid transfer proteins (BLTPs).

The research elucidates how BLTP function is regulated at endoplasmic reticulum (ER) and plasma membrane contact sites, with focus on the TWEEK complex and its role in mediating lipid transfer during cellular processes such as phagocytosis. The investigator will resolve the hierarchy of tether proteins (SPIGOT and RACK1) using the contact-FP system, investigate recruitment and retention mechanisms at ER-PM contact sites, and define how BLTP-mediated lipid transfer itself is regulated. The work leverages an established Drosophila model in which TWEEK's function in phagocytic astrocytes provides an in vivo readout of BLTP activity and regulation. Prior foundational work includes high-resolution cryo-EM structural characterization (2.7 Å resolution) of the C. elegans TWEEK homolog LPD3 and identification of key binding partners.

Performance occurs in Aurora, Colorado. The award runs from August 1, 2026, through March 31, 2031. The assistance type is Project Grant.

Abstract

How is bridge-like lipid transfer protein (bltp) function regulated? Cells and cellular organelles are defined by phospholipid bilayer membranes. Most bilayer lipids originate in the endoplasmic reticulum (ER), but how are they precisely delivered to these various cellular membranes? Recently, a novel class of proteins known as bltps has been identified. Localizing to sites of close contact between the ER and other membranes, these proteins function as molecular highways for lipid transport, utilizing their unique structure to transfer bulk lipids. However, the mechanisms regulating their activity under physiological conditions in vivo are not yet defined. In my postdoctoral work, i identified and characterized the bltp tweek, demonstrating its critical role in mediating membrane expansion during drosophila astrocyte phagocytosis. Loss of tweek disrupts ER-plasma membrane (ER-PM) contact sites and impairs phagosomal expansion, highlighting the crucial role of lipid transfer in this key developmental process. To gain insight into its function, we resolved the high-resolution cryo-EM (2.7 a˚) structure of the c. Elegans tweek homolog, LPD−3, providing critical insights into the molecular basis of lipid transfer and identifying key binding partners. Building on these foundational discoveries, my lab is uniquely positioned to elucidate the mechanisms governing bltp-mediated lipid transfer. This proposal will investigate both how the tweek complex is recruited to, retained at, and dynamically regulates ER-PM contact sites, and how bltp-mediated lipid transfer itself is regulated. We will leverage an established drosophila model, where tweek's function in phagocytic astrocytes provides a powerful in vivo readout of bltp activity and regulation. Specifically, we will resolve the hierarchy of tethers (spigot and RACK1) using the contact-FP system to define ER-PM contact site localization and tethering. We will then determine how bltp-mediated lipid transfer is regulated by characterizing the function of the novel, associated scramblase TMEM170, using structure-guided genetics in drosophila and quantitative lipidomic analysis on purified LPD−3 complexes from TMEM170 mutant c. Elegans to establish its essential role in lipid acquisition. To obtain a family-wide view, we will use the fast growth and scale of yeast as a high-throughput platform to map the interactome, determine the diverse lipid cargo, and resolve the full structures of all bltp homologs. This integrated approach, combining genetics, cell biology, and biochemistry, will illuminate the fundamental principles governing bltp-mediated lipid transfer during the dynamic process of phagocytosis and will establish a framework for understanding how lipid dynamics are regulated to support diverse cellular functions.