a, Overview of the C-terminal surface area (in blue) that is not masked by carbohydrate. Brassinolide is shown in yellow, the island domain in orange, and genetic alleles connected in magenta, b, Analytical gel-filtration 280 nm absorbance trace. The free ectodomain eluates as a monomer (black line), as does a putative complex with brassinolide (red line). Void (V0) and total volume (Vt) are shown together with elution volumes for molecular weight standards (A, aldolase, MW 158,000 Da; B, conalbumin, MW 75,000 Da). The estimated molecular weight for the monomer peak is ~125 kDa. The approximate molecular weight of the purified BRI1 is 110 kDa.