The reticulon homology domain of Pex30 generates membrane curvature at ER subdomains for lipid droplet biogenesis

Abstract

Lipid droplets (LDs) are dynamic organelles that store neutral lipids and form in the endoplasmic reticulum (ER) membrane. Formation of new LDs is a controlled process and requires proteins with specific functions to form and grow from the ER membrane without any defect. In vitro studies have suggested a role for membrane curvature in LD emergence from the ER. Here, we use the membrane-shaping protein Pex30 to investigate the impact of ER membrane curvature on LD biogenesis and morphology. We modified the reticulon homology domain (RHD) of Pex30, which is responsible for tubulating the ER membrane, by extending the short hairpin transmembrane domains (TMD). The Pex30 (TMD) mutants cannot tubulate the ER membrane and generate less local membrane curvature that WT Pex30. Additionally, these mutants are unable to restore delayed LD biogenesis observed in cells devoid of Pex30. Our results indicate that Pex30 RHD generates local membrane curvature at ER subdomains that drives formation of new LDs.