Advancing Chemoenzymatic Synthesis and Covalent Immobilization of a Comprehensive Ganglio-glycosphingolipid Library Enables Functional Multiplex Bead Assays

Ganglio-series glycosphingolipids (ganglio-GSLs) are biologically important glycolipids comprising a glycan of a ganglio-series nature and a lipid called ceramide. The glycan component often contains one or more sialic acid residues. Accesses to structurally defined ganglio-GSLs remain limited due to their structural complexity and synthetic challenges, hindering both functional studies and therapeutic applications. To overcome the challenges, we report herein a scalable chemoenzymatic total synthesis strategy for the construction of the most comprehensive library of ganglio-GSLs to date. A chiral pool approach was developed for synthesizing simple glycosylsphingosines with desired sphingosine lengths (d18:1 or d20:1) from inexpensive d-xylose. Complex glycosylsphingosines were prepared using enzyme assembly synthetic map (EASyMap)-guided streamlined one-pot multienzyme (OPME) and stepwise OPME (StOPMe) glycosylation strategies facilitated by designing mutants with improved catalytic efficiencies for two key glycosyltransferases (CjCgtA and human ST6GALNAC5). Ganglio-GSLs containing a terminal primary amino group were then prepared by chemical acylation, enabling their covalent immobilization on magnetic beads to form a novel comprehensive ganglio-GSL-bead library encompassing 0-, a-, b-, and c-series ganglio-GSLs including structures containing up to five sialic acid residues with different (α2-3/6/8) sialyl linkages. Multiplex binding assays revealed that ganglio-GSLs exhibit distinctive interactions with glycan-binding proteins including plant lectins, antiganglioside antibodies, bacterial toxins, galectins, and human and mouse siglecs. The integration of streamlined chemoenzymatic total synthesis strategies, glycosyltransferase engineering, covalent immobilization of GSL analogs, and a multiplex assay platform enables synthesis and high-throughput studies of previously difficult-to-obtain ganglio-GSLs. It is broadly applicable to help advance glycobiology and develop GSL-based diagnostics and therapeutics.