A system-wide analysis of lipid transfer proteins delineates lipid mobility in human cells

Abstract

Lipid transfer proteins (LTPs) maintain the specialized lipid compositions of biological membranes, and many are associated with disease. In eukaryotes, they support organellar functions by transporting lipids between compartmentalized metabolic pathways. However, for the majority of the hundreds human LTPs, the cargoes remain unknown. We combined biochemical, lipidomic and computational methods to characterize LTP-lipid complexes assembledin celluloand in anin vitrobiochemical assay. We identified bound lipids for about half of the LTPs analysed, and confirmed known cargoes, while discovering new ones for most LTP families. This work represents a systematic resource that captures the general principles of non-vesicular lipid transport in humans. The specificity of LTP for lipids involves not only the recognition of specific head groups, but also of specific fatty acids. This selectivity defines lipid species within a lipid class with different metabolic or functional fates. The generalized ability of LTPs to form complexes with more than one classe of lipids delineates new relationships between lipids and regulatory mechanisms that may contribute to the coordination of metabolism between different organelles. This work represents a proof of principle and a resource for follow-up analyses in different cell types or following different cellular perturbations or stimulations.

A Membrane-Assisted Mechanism for the Release of Ceramide from the CERT START Domain

“…The in silico models suggest that CERT-mediated ceramide transport requires direct interaction with phosphatidylcholine in the membrane and temporarily at least partial uptake in its hydrophobic cavity. As binding to PC is new, we set out to validate this experimentally by integrating and reanalyzing data from our recent systematic biochemical analysis of LTP cargos . We overexpressed CERT in HEK293 cells and, after biochemical purification, characterized CERT-associated lipids by LC-MS/MS-based lipidomics (Figure ).…”

“…As binding to PC is new, we set out to validate this experimentally by integrating and reanalyzing data from our recent systematic biochemical analysis of LTP cargos. 66 We overexpressed CERT in HEK293 cells and, after biochemical purification, characterized CERT-associated lipids by LC-MS/MS-based lipidomics ( Figure 7 ). We have identified PC (34:1) and PC (32:1) to form stable complexes with CERT ( Table S8 ).…”