Enzymatic sulphation of mucus glycoprotein in rat sublingual salivary gland

Characterization of an N-acetylglucosamine-6-O-sulfotransferase from human respiratory mucosa active on mucin carbohydrate chains

A microsomal GlcNAc-6-O-sulfotransferase activity from human bronchial mucosa, able to transfer a sulfate group from adenosine 3'-phosphate 5'-phosphosulfate onto methyl-N-acetylglucosaminides or terminal N-acetylglucosamine residues of carbohydrate chains from human respiratory mucins, has been characterized. The reaction products containing a terminal HO3S-6GlcNAc were identified by high performance anion-exchange chromatography. Using methyl-beta-N-acetylglucosaminide as a substrate, the optimal activity was obtained with 0.1% Triton X-100, 30 mM NaF, 20 mM Mn2+, 5 mM AMP in a 30 mM MOPS (3-(N-morpholino) propanesulfonic acid) buffer at pH 6.7. The apparent Km values for adenosine 3'-phosphate 5'-phosphosulfate and methyl-beta-N-acetylglucosaminide were observed at 9.1 x 10(-6) M and 0.54 x 10(-3) M, respectively. The enzyme had more affinity for carbohydrate chains with a terminal GlcNAc residue than for methyl-beta-N-acetylglucosaminide; it was unable to catalyze the transfer of sulfate to position 6 of the GlcNAc residue contained in a terminal Galbeta1-4GlcNAc sequence. However, oligosaccharides with a nonreducing terminal HO3S-6GlcNAc were substrates for a beta1-4 galactosyltransferase from human bronchial mucosa. These data point out that GlcNAc-6-O-sulfotransferase must act before beta1-4 galactosylation in mucin-type oligosaccharide biosynthesis.

Characterization of a sulfotransferase from human airways responsible for the 3-O-sulfation of terminal galactose in N-acetyllactosamine-containing mucin carbohydrate chains

A galactose 3-O-sulfotransferase activity able to transfer a sulfate group from adenosine 3'-phosphate 5'-phosphosulfate to methyl galactosides or terminal N-acetyllactosamine-containing carbohydrate chains from human respiratory mucins was characterized in microsomal fractions prepared from human respiratory mucosa. The reaction products, methyl alpha- or beta-galactose 3-sulfate and three oligosaccharide alditols containing the sequence HSO3-3Gal beta 1-4GlcNAc beta 1-6GalNAc-itol were identified by high performance anion-exchange chromatography. Using methyl beta-galactoside as a substrate, the optimum activity was obtained with 0.1% Triton X-100, 30 mM NaF, 20 mM Mn2+, and 10 mM AMP in a 30 mM 2-(N-morpholino)ethanesulfonic acid buffer at pH 6.1. The apparent Km for methyl beta-galactoside and for adenosine 3'-phosphate 5'-phosphosulfate were observed at 0.69 x 10(-3) M and at 4 x 10(-6) M respectively. This sulfotransferase is different from that responsible for sulfatide synthesis.

Effect of lipids on glycoprotein sulphotransferase activity in rat submandibular salivary glands

Although glycoprotein sulphation has been implicated in the processing of salivary mucin, little is known about the regulation of the enzyme responsible for this event. Using desulphated glycoprotein as sulphate acceptor, the glycoprotein sulphotransferase (GPST) from Golgi membranes of submandibular salivary gland was used to study the effect of various lipids on its activity. The GPST activity in the Golgi membrane was 0.7 pmol/mg protein per min and the activity was extractable by Triton S-100. The Km of the solubilized GPST for glycoprotein and 3'-phosphoadenosine 5'-phosphosulphate (PAPS) were 11 and 0.2 microM, respectively. Among the various lipids tested, phosphatidylinositol and sphingosine stimulated the GPST activity, while other lipids such as sphingomyelin, phosphatidylcholine and phosphatidylserine did not produce a significant effect. At 12 mol% (when expressed as mol% of sphingosine to total phospholipids plus Triton X-100) of sphingosine concentration, the enzyme activity was increased nearly 1.7-fold. The stimulatory effect of sphingosine was accompanied by a significant decrease in Km for glycoprotein from 11 to 2 microM but the increase in Vmax was small. In contrast, the sphingosine effect did not change the Km for PAPS but increased the Vmax nearly two fold. Of the two sphingosine analogues tested, threosphinganine and erythrosphinganine had a lesser stimulatory effect than sphingosine. Stearylamine was partially active, whereas the amino acids (glutamate, aspartate, glutamine, asparagine and serine) were not. These observations and our earlier finding of tyrosylprotein sulphotransferase inhibition by sphingosine demonstrate diverse sphingosine effects on the post-translational sulphation involved in the processing of salivary proteins and suggest an important role for sphingosine in the regulation of salivary protein sulphation.

Silver staining of extensively glycosylated proteins on sodium dodecyl sulfate-polyacrylamide gels: enhancement by carbohydrate-binding dyes

Two methods are described for detecting less than 1 microgram of highly glycosylated proteins, such as mucins, on sodium dodecyl sulfate-polyacrylamide gels. They combine commonly employed periodic acid-Schiff (PAS) and Alcian blue dyes with silver stain. Carbohydrate prestaining renders mucins more cationic and favors greater complexation with ionic silver. Comparisons of different mucin samples stained either with PAS-silver or alcian blue-silver indicate differential staining between the two techniques. Such differences may, in part, be due to an affinity of Alcian blue for sulfated glycoproteins. These two staining protocols when used in conjunction with silver staining alone are particularly valuable for assessing sample purity and for detecting contaminating proteins during mucin purification protocols.