All cellular organelles have characteristic shapes. The endoplasmic reticulum (ER) is particularly intriguing, as it contains a network of interconnected tubules. The tubules have high membrane curvature in cross-section, generated by the reticulon and REEP protein families, but how these proteins cause curvature is poorly understood. In a new study published in Nature Communications, the Rapoport Lab shows that REEPs form homodimers and use their amphipathic helix and trans-membrane segments to generate high membrane curvature that can even lead to the formation of lipoprotein particles.