Following sugar patterns in search of galectin function

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Abstract
Through evolution, glycans have been selected as a class of biomolecules tasked with facilitating information exchange at the cellular boundary (1). Presented as attachments on membrane proteins or linked directly to lipids embedded in the plasma membrane of cells, glycans serve as recognition elements for glycan binding proteins, such as lectins or antibodies, and mediate essential biological processes, ranging from cell–cell adhesion and migration to more complex events associated with organismal development and function. Not surprisingly, glycans also contribute to disease development and progression and have been linked to a large number of pathophysiological processes, including infectious diseases, cancer, or autoimmune disorders (2). However, glycans and their cognate lectin counter-receptors are still rarely considered as suitable drug targets (3). In PNAS, Xiao et al. (4) employ cell-surface mimetic models to dissect how glycan receptor organization in cellular membranes influences functional association with galectins, a family of human lectins (5). Among their many functions, galectins have been identified to serve as important extracellular modulators of immune responses and have been positively correlated with increased aggressiveness of tumors (6). As such, galectins are certainly enticing targets for medical intervention (7); however, the broad functional polymorphism observed for the galectin family members necessitates that principles governing their interactions with glycan receptors be established first to guide the design of selective galectin-targeting therapeutics. The structures of glycans define their molecular interactions with lectins and all members of the galectin family generally recognize glycans containing β-galactose residues (8), with modifications such as sialylation (9) or sulfation (10) providing addition affinity. As is typical for most lectins, galectins show weak (high micromolar to low millimolar) affinity for simple soluble β-galactosides, such as lactose. The much higher-affinity interactions (submicromolar) observed for galectins in biological settings are the result of their ability to engage ensembles of glycans … [↵][1]1Email: kgodula{at}ucsd.edu. [1]: #xref-corresp-1-1

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