Structure of apolipoprotein B100 bound to the low-density lipoprotein receptor.

Apolipoprotein B100 (apoB100) is a structural component of low-density lipoprotein (LDL) and a ligand for the LDL receptor (LDLR). Mutations in apoB100 or in LDLR cause familial hypercholesterolaemia, an autosomal dominant disease that is characterized by a marked increase in LDL cholesterol (LDL-C) and a higher risk of cardiovascular disease. The structure of apoB100 on LDL and its interaction with LDLR are poorly understood. Here we present the cryo-electron microscopy structures of apoB100 on LDL bound to the LDLR and a nanobody complex, which can form a C-symmetric, higher-order complex. Using local refinement, we determined high-resolution structures of the interfaces between apoB100 and LDLR. One binding interface is formed between several small-ligand-binding modules of LDLR and a series of basic patches that are scattered along a β-belt formed by apoB100, encircling LDL. The other binding interface is formed between the β-propeller domain of LDLR and the N-terminal domain of apoB100. Our results reveal how both interfaces are involved in LDL dimer formation, and how LDLR cycles between LDL- and self-bound conformations. In addition, known mutations in either apoB100 or LDLR, associated with high levels of LDL-C, are located at the LDL-LDLR interface.