BPS2026 – Molecular determinants of caveolin interactions with membranes

Caveolins are the major structural proteins of small (60–80 nm), cholesterol-rich plasma membrane (PM) invaginations called caveolae. These structures participate in many diverse cellular processes including mechano-adaptation, lipid sorting, and signal scaffolding. Accordingly, caveolin mutations are associated with diseases of dysfunctional signaling and impaired lipid trafficking, highlighting the importance of these proteins in cellular organization and physiology. Critically, the molecular mechanisms by which caveolins control membrane organization and contribute to physiological processes are unknown, in part because the molecular architecture of these proteins has remained speculative. The recently determined cryo-EM structure of the Caveolin-1 8S (Cav1-8S) complex solved this knowledge gap, revealing that caveolin assembles into a unique, tightly packed 11-mer disc with a 14-nm-diameter hydrophobic surface and a central beta barrel. The unusual physical characteristics of Cav1-8S suggest a novel mode of interactions with lipids and other proteins at the PM. To investigate caveolin-membrane interactions, we combined computational molecular modeling and model membrane experiments to reveal that Cav1-8S inserts deeply into one leaflet of a lipid bilayer via its large hydrophobic surface. This insertion leads to membrane curvature, induced by caveolin’s reorganization of lipid acyl chains, and sequestering cholesterol to its hydrophobic surface and beta barrel. The cellular context for these interactions and how they contribute to PM organization is unknown. Based on computational predictions, we hypothesize that unique structural features of Cav1-8S bend cellular membranes, modulate membrane biophysical properties, and contribute to cholesterol homeostasis. We test these hypotheses through cell-based experiments and reconstitution of recombinantly purified Cav1-8S into biomimetic membrane models. Overall, our findings suggest a novel mechanism by which Cav1-8S shapes membranes, sequesters cholesterol, and sorts lipids, uncovering how the unique properties of Caveolin-1 modulate the biophysical properties and homeostasis of the PM.