sb8b00225_si_002.mpg (81.2 MB)
De Novo-Designed α‑Helical Barrels as Receptors for Small Molecules
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posted on 2018-06-26, 00:00 authored by Franziska Thomas, William M. Dawson, Eric J. M. Lang, Antony J. Burton, Gail J. Bartlett, Guto G. Rhys, Adrian J. Mulholland, Derek N. WoolfsonWe
describe de novo-designed α-helical barrels
(αHBs) that bind and discriminate between lipophilic biologically
active molecules. αHBs have five or more α-helices arranged
around central hydrophobic channels the diameters of which scale with
oligomer state. We show that pentameric, hexameric, and heptameric
αHBs bind the environmentally sensitive dye 1,6-diphenylhexatriene
(DPH) in the micromolar range and fluoresce. Displacement of the dye
is used to report the binding of nonfluorescent molecules: palmitic
acid and retinol bind to all three αHBs with submicromolar inhibitor
constants; farnesol binds the hexamer and heptamer; but β-carotene
binds only the heptamer. A co-crystal structure of the hexamer with
farnesol reveals oriented binding in the center of the hydrophobic
channel. Charged side chains engineered into the lumen of the heptamer
facilitate binding of polar ligands: a glutamate variant binds a cationic
variant of DPH, and introducing lysine allows binding of the biosynthetically
important farnesol diphosphate.