Open or closed: N-Glycosyl oxyamine versus open-chain glycosyl oxime is the key to protein recognition on glyconanoparticles. Unprotected glycans are captured by oxime formation with a novel bifunctional reagent and the resulting glycan-linker conjugates are anchored to gold nanoparticles (AuNPs). These glyconanoparticles maintain the structural integrity of glycans in the study of protein–carbohydrate interactions (see figure).
Nanoparticles functionalized with glycans are emerging as powerful solid-phase chemical tools for the study of protein–carbohydrate interactions using nanoscale properties for detection of binding events. Methods or reagents that enable the assembly of glyconanoparticles from unprotected glycans in two consecutive chemoselective steps with meaningful display of the glycan are highly desirable. Here, we describe a novel bifunctional reagent that 1) couples to glycans by oxime formation in solution, 2) aids in purification through a lipophilic trityl tag, and 3) after deprotection then couples to gold nanoparticles through a thiol. NMR studies revealed that these oximes exist as both the open-chain and N-glycosyl oxy-amine tautomers. Glycan-linker conjugates were coupled through displacement of ligands from preformed, citrate-stabilized gold nanoparticles. Recognition of these glycans by proteins was studied with a lectin, concanavalin A (ConA), in an aggregation assay and with a processing enzyme and glucoamylase (GA). We demonstrate that the presence of the N-glycosyl oxy-amines clearly enables functional recognition in sharp contrast to the corresponding reduced oxy-amines. This concept is then realized in a novel reagent, which should facilitate nanoglycobiology by enabling the operationally simple capture of glycans and their biologically meaningful display.