Extended Data Fig. 1: Biochemical characterization of LDL, LDLR and legobody.

a, Schematic of the resolved (hot pink) and unresolved (light pink) regions of LDLR extracellular domain labelled with modules LA1 (residues 25–65), 2 (residues 66–106), 3 (residues 107–145), 4 (residues 146–186), 5 (residues 195–233), 6 (residues 234–272), and 7 (residues 274–313), EGF-A (residues 314–353), -B (residues 354–393), -C (residues 667–712), and the β-propeller (residues 398–663). A single point mutation (D193A) in the LDLR construct was made to prevent proteolytic cleavage. b, Biolayer interferometry of LDL binding to LDLR with nanomolar affinity. c, Independent biological replicate of LDL binding to LDLR in the absence (left) and presence (right) of legobody. d, Mass photometry of LDLR. The calculated molecular weight of LDLR protein is 90 kDa (Std. Dev. 17 kDa). e, Size-exclusion chromatogram of purified human LDL alone (black), with an excess of LDLR (blue), with an excess of both LDLR and legobody (red), and controls LDLR alone (green) and legobody alone (grey). f, Biolayer interferometry of LDL binding to nanobody 4 with nanomolar affinity. g, Coomassie-stained, SDS–PAGE of size-exclusion eluant fractions of LDL+LDLR+legobody. SDS–PAGE for this exact SEC was performed once. e,g, Red asterisk (*) denotes the fraction prepared for cryo-EM. The SEC peaks are labelled accordingly: the complex peak (A), excess LDLR peak (B), and excess legobody peak (C). h, Representative cryo-EM micrograph from the selected fraction, n = 36,873. The inset shows the dimeric LDL/LDLR/legobody complex. Scale bars, 40 nm.