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Characterization and Carbohydrate Specificity of Pradimicin S

Shahzad-ul-Hussan, Syed, Ghirlando, Rodolfo, Dogo-Isonagie, Cajetan I., Igarashi, Yasuhiro, Balzarini, Jan, Bewley, Carole A.
Journal of the American Chemical Society 2012 v.134 no.30 pp. 12346-12349
Human immunodeficiency virus 1, anti-infective properties, antibiotics, binding sites, calcium, glycoproteins, inhibitory concentration 50, mannose, models, nuclear magnetic resonance spectroscopy, oligomerization, trisaccharides, ultracentrifugation, water solubility
The pradimicin family of antibiotics is attracting attention due to its anti-infective properties and as a model for understanding the requirements for carbohydrate recognition by small molecules. Members of the pradimicin family are unique among natural products in their ability to bind sugars in a Ca²⁺-dependent manner, but the oligomerization to insoluble aggregates that occurs upon Ca²⁺ binding has prevented detailed characterization of their carbohydrate specificity and biologically relevant form. Here we take advantage of the water solubility of pradimicin S (PRM-S), a sulfated glucose-containing analogue of pradimicin A (PRM-A), to show by NMR spectroscopy and analytical ultracentrifugation that at biologically relevant concentrations, PRM-S binds Ca²⁺ to form a tetrameric species that selectively binds and engulfs the trisaccharide Manα1–3(Manα1–6)Man over mannose or mannobiose. In functional HIV-1 entry assays, IC₅₀ values of 2–4 μM for PRM-S corrrelate with the concentrations at which oligomerization occurs as well as the affinities with which PRM-S binds the HIV surface envelope glycoprotein gp120. Together these data reveal the biologically active form of PRM-S, provide an explanation for previous speculations that PRM-A may contain a second mannose binding site, and expand our understanding of the characteristics that can engender a small molecule with the ability to function as a carbohydrate receptor.