Molecular design of fluorescent labeled glycosides as acceptor substrates for sialyltransferases

Abstract

A series of dansyl-labeled glycosides with di-, tetra-, and hexasaccharides carrying the terminal iV-acetyllactosamine (LacNAc) sequence were synthesized as acceptor substrates for α2,6-and α2,3-sialyltransferases. As an alternative design, dansyl-labeled LacNAc glycoside carrying a long-spacer linked glycan was engineered by replacement of the LacNAc or lactose units with an alkyl chain. In addition, we designed a dansyl-labeled bi-antennary LacNAc glycoside as an iV-linked oligosaccharide mimetic, such as asialo- α1-acid glycoprotein. The kinetic parameters for the transfer reaction of synthesized dansyl-labeled glycosides by sialyltransferases were determined by the fluorescent HPLC method. The catalytic efficiencies (V max/Km) of acceptor substrates carrying the terminal LacNAc sequence with various length glycans in the array for α2,6-and α2,3-sialyltransferases decreased in a glycan lengthdependent manner. Furthermore, of the acceptor substrates tested, dansyl-labeled bi-antennary LacNAc glycoside displayed the most favorable Km value for α2,6-and α2,3-sialyltransferases.