ISSN:
1573-4986
Keywords:
Synthetic oligosaccharides
;
inhibitors
;
N-glycans
;
N-acetylglucosaminyltransferase
;
biosynthesis
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract UDP-GlcNAc: Manα1-6R β(1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man‴α1-6(GlcNAc″β1-2Man′α1-3)Manβ-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in β1-2 linkage to the 2‴-OH of the Man‴α1-6 residue. The 2‴-deoxy analogue is a competitive inhibitor (K i=0.13mm). The 2‴-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3‴-, 4‴- and 6‴-OH groups are not essential for binding or catalysis since the 3‴-, 4‴- and 6‴-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3‴-position to pentyl and substituted pentyl groups causes competitive inhibition (K i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3‴-O-(4,4-azo)pentyl group and a 3‴-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man‴α1-6 residue are essential for binding although the 2‴- and 3‴-OH face the catalytic site of the enzyme. The 4-OH group of the Manβ-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Manβ- substrate analogue. The data are compatible with our previous observations that a ‘bisecting’N-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3′-OH of the Man′α1-3 is an essential group for GlcNAc-T II since the 3′-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAcβ1-2Manα1-3Manβ-O-octyl is a good inhibitor (K i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAcβ1-2Manβ1-3Manβ- arm of the branched substrate to the enzyme is essential for catalysis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00731220
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