Escherichia coli β-galactosidase unexpectedly cleaves the hexasaccharide Galβ1-4GlcNAcβ1-3(Galβ1-4GlcNAcβ1-6)Galβ1-4GlcNAc without branch specificity

Publisher Website
Google Scholar
Abstract
The branch specificity of Escherichia coli β-galactosidase (EC 3.2.1.23) was studied by analyzing the cleavage of the branched hexasaccharide Galβ1-4GlcNAcβ1-3(Galβ1-4GlcNAcβ1-6)[14C(U)]Galβ1-4GlcNAc (1). This hexasaccharide was cleaved to pentasaccharides Galβ1-4GlcNAcβ1-3(GlcNAcβ1-6)[14C(U)]Galβ1-4GlcNAc (3) and GlcNAcβ1-3(Gal-β1-4GlcNAcβ1-6)[14C(U)]Galβ1-4GlcNAc (4) without any appreciable branch specificity. Even the further conversions of the pentasaccharides 3 and 4 into the tetrasaccharide GlcNAcβ1-3(GlcNAcβ1-6)[14C(U)]Galβ1-4GlcNAc seemed to proceed at similar rates, without any appreciable branch specificity. In marked contrast to the hexasaccharide 1, the pentasaccharide Galβ1-4GlcNAcβ1-3(Galβ1-4GlcNAcβ1-6)[14C(U)]Gal (2), missing the reducing end GlcNAc, is known to be cleaved selectively at the 6-branch; this finding was confirmed in the present study. The different behaviour of hexasaccharide 1 and pentasaccharide 2 reflects differences in the reactivity of their 6-branches; the preferred conformations of these closely related molecules may be quite different.Key words: Escherichia coli β-galactosidase, branch-specific cleavage, random cleavage, oligo-N-acetyllactosaminoglycans, enzymatic in vitro synthesis.

This publication has 7 references indexed in Scilit: