Encoding biological recognition in a bicomponent cell-membrane mimic

Abstract

Self-assembling dendrimers have facilitated the discovery of periodic and quasiperiodic arrays of supramolecular architectures and the diverse functions derived from them. Examples are liquid quasicrystals and their approximants plus helical columns and spheres, including some that disregard chirality. The same periodic and quasiperiodic arrays were subsequently found in block copolymers, surfactants, lipids, glycolipids, and other complex molecules. Here we report the discovery of lamellar and hexagonal periodic arrays on the surface of vesicles generated from sequence-defined bicomponent monodisperse oligomers containing lipid and glycolipid mimics. These vesicles, known as glycodendrimersomes, act as cell-membrane mimics with hierarchical morphologies resembling bicomponent rafts. These nanosegregated morphologies diminish sugar-sugar interactions enabling stronger binding to sugar-binding proteins than densely packed arrangements of sugars. Importantly, this provides a mechanism to encode the reactivity of sugars via their interaction with sugar-binding proteins. The observed sugar phase-separated hierarchical arrays with lamellar and hexagonal morphologies that encode biological recognition are among the most complex architectures yet discovered in soft matter. The enhanced reactivity of the sugar displays likely has applications in material science and nanomedicine, with potential to evolve into related technologies.

Keywords: Janus glycodendrimers; atomic force microscopy; galectin; lipid rafts; nanosegregation.

Fig. 1.

Molecular structures of JGDs. Structures and short nomenclatures are shown for (Top) high-sugar density JGD-1_Lac, JGD-2_Lac, and JGD-4_Lac, and sequence-defined JGD(3/1_Lac), JGD(5/1_Lac²), JGD(5/1_Lac³), JGD(6/1_Lac); (Bottom) JGD(8/1_Lac^2S), JGD(8/1_Lac^3S), JGD(8/1_Lac^2L), and JGD(8/1_Lac^3L).

Fig. 2.

Molecular architecture JGDs containing defined glycan sequence and density. (A) Sequence-defined JGDs with different Lac density, sequence, and linker length. (B) Schematic representation of JGD building blocks. (C) Summary of aggregation assay data using GDSs from self-assembly of sequence-defined JGDs (Lac = 0.1 mM, 900 μL) with Gal-1 (1 mg·mL⁻¹, 100 μL), Gal-8S (1 mg·mL⁻¹, 100 μL), and (Gal-1)₄–GG (1 mg·mL⁻¹, 100 μL). Color codes for galectins: Gal-1, red; Gal-8S, blue; (Gal-1)₄–GG, green. N and C represent the N and C termini of proteins. For selected examples symbols used for significant difference (P values by Student’s t test) are: “n.s.” for P > 0.05 (for statistically nonsignificant) and “*” for P < 0.05 (for statistically significant).

Fig. 3.

Illustration of combined AFM, FFT, and modeling methodology for structural analysis.

Fig. 4.

Surface topology of GDS formed by self-organization of JGDs depends on glycan sequence and density. (A) JGD-2_Lac; (B) JGD-4_Lac; (C) JGD(6/1_Lac); (D) JGD(8/1_Lac^3L). (B–D, Inset) FFT of AFM phase images. Color code: red, sugars; blue, hydrophilic 3EO; green, hydrophobic alkyl.

Fig. 5.

Models of nanosegregated bilayer structures. (A and B) Models of JGD-4_Lac: (A) single sugar cluster comprising three molecules on each side of the bilayer; (B) sugar clusters in bilayer. (C) FFT of the AFM phase image of JGD(8/1_Lac^3L) (Fig. 4D) shows multiple features consistent with formation of a hexagonal array. Blue, yellow, and green circles indicate (10), (11), and (20) features, respectively. The theoretical ratio a:b:c for a hexagonal array is 1:√3(=1.73):2; the observed ratio a:b:c is 1:1.75:2.04. (D, Left) Model of hexagonal nanosegregation and (D, Right) AFM height image of JGD(8/1_Lac^3L). (E) Top view of bilayer model with all Lac moieties and three highlighted JGD(8/1_Lac^3L) molecules in CPK view. (F) Side view of a column of the bilayer of JGD(8/1_Lac^3L).