Abstract
Efficient delivery of specific cargos in vivo poses a major challenge to the secretory pathway, which shuttles products encoded by ∼30% of the genome. Newly synthesized protein and lipid cargos embark on the secretory pathway via COPII-coated vesicles, assembled by the GTPase SAR1 on the endoplasmic reticulum (ER), but how lipid-carrying lipoproteins are distinguished from the general protein cargos in the ER and selectively secreted has not been clear. Here, we show that this process is quantitatively governed by the GTPase SAR1B and SURF4, a high-efficiency cargo receptor. While both genes are implicated in lipid regulation in humans, hepatic inactivation of either mouse Sar1b or Surf4 selectively depletes plasma lipids to near-zero and protects the mice from atherosclerosis. These findings show that the pairing between SURF4 and SAR1B synergistically operates a specialized, dosage-sensitive transport program for circulating lipids, while further suggesting a potential translation to treat atherosclerosis and related cardio-metabolic diseases.