Significance: The seminal fluid mosaic model of the cell membranes suggests a lipid bilayer sea, in which cholesterol, proteins, glycoconjugates, and other components are swimming. Complementing this view, a microsegregated rafts model predicts clusters of components that function as relay stations for intracellular signaling and trafficking. However, elucidating the arrangement of glycoconjugates responsible for communication and recognition between cells, and cells with proteins remains a challenge. Herein, designed dendritic macromolecules are shown to self-assemble into vesicles that function as biological-membrane mimics with controlled density of sugar moieties on their periphery. Surprisingly, lowering sugar density elicits higher bioactivity to sugar-binding proteins. This finding informs a design principle for active complex soft matter with potential for applications in cellular biology and nanomedicine.