Novel enzymatic synthesis of spacer-linked Pk trisaccharide targeting for neutralization of Shiga toxin

A novel alkyl spacer-conjugated derivative of Pk trisaccharide (Pk), one of the active receptors of Shiga toxins (Stxs; Stx1 and Stx2) produced by pathogenic Escherichia coli (STEC), was designed and synthesized by a combination of cellulase-mediated condensation from Trichoderma reesei and α1,4-galactosyltransferase (LgtC) from Neisseria gonorrhoeae. The specific activity of N. gonorrhoeae LgtC was 66 U/mg, which was 13-fold higher than that from N. meningitidis expressed in E. coli. 5-trifluoroacetamidopentyl-β-Pk (TFAP-Pk) was synthesized (yield of 86%, based on the amount of TFAP-lactose added) and its binding to Stx1a-B and Stx2a-B was evaluated. The dissociation constants (KDs) of Stx1a-B and Stx2a-B to the spacer-linked Pk, immobilized on a CM5 sensor chip, were 6.8 × 10−6 M (kon = 4.1 × 101 M−1 S−1, koff = 2.8 × 10−4 S−1) and 2.2 × 10−5 M (kon = 3.9 × 102 M−1 S−1, koff = 8.6 × 10−3 S−1), respectively. This result suggests that the monovalent Pk-derivative, conjugated to a pentylamino group, represents a promising Stx-neutralizing agent. This cellulase-mediated condensation using cellulase and glycosyltransferase is a valuable tool for the synthesis of spacer-linked oligosaccharide.