Differences in the glycosylation of rat submandibular kallikreins

Organic secretion in ductal cells of the sublingual salivary gland of ferret: Histochemical observations

The presence of organic secretion in ductal cells of the sublingual salivary gland of ferret has been questioned, which prompted the present investigation. Paraffin or cryostat sections from aldehyde fixed or quenched sublingual glands of this species were tested for some amino acid residues, mucosubstances, oxidative and hydrolytic enzymes, and lectins. The glands showed inconspicuous ducts of simple appearances on routine histology. The histochemical procedures, however, revealed a granulated substance in the apical (periluminal) region of ductal cells, which contained tryptophan, disulphides, neutral mucosubstances, αFuc and GalNAc, and showed chloroacetate esterase activity. Occurrence of the substance varied between different ducts of the same gland and/or cells of the same duct. The ductal cells also showed diffuse peroxidase and acid phosphatase, and Golgi-like thiamine pyrophosphatase activities. Acetylcholinesterase-positive nerve fibres embraced the ducts. The results support a particular localisation of protein-bound amino acid residues and enzymatic catalytic activities indicative of organic secretion, possibly tissue kallikrein, in sublingual ductal cells of ferret.

O-linked glycosylation occurs on basic parotid salivary proline-rich proteins

Interactions between salivary glycoproteins and many oral bacteria have been shown to depend on O-linked glycans on salivary glycoproteins. Basic proline-rich proteins form the largest group of proteins within human parotid saliva. In the present study human parotid salivary glycoproteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis or two-dimensional electrophoresis, electroblotted onto nitrocellulose and probed with two biotin-labelled lectins from Maclura pomifera (MPA) and Arachis hypogaea (PNA) which are specific for O-linked (galactose beta 1,3 N-Acetylgalactosamine) glycans. Lectin binding was detected with avidin-biotin complex and enhanced chemiluminescence. Two-dimensional electrophoresis in combination with lectin binding indicated that only basic parotid salivary glycoproteins bind the lectin MPA. Following removal of terminal sialic acid residues by sialidase digestion the same glycoproteins were detected by the lectin PNA. Glycosidase digestion with endo-alpha-N-acetylgalactosaminidase (O-glycanase) in conjunction with sialidase eliminated MPA binding. Taken together these results indicate that many basic parotid salivary glycoproteins contain O-glycans, all of which are sialylated.

Lectin binding studies of parotid salivary glycoproteins in Sjögren's syndrome

Human parotid salivas were collected from patients with secondary Sjögren's syndrome and controls without disease or with drug-induced xerostomia. Parotid glycoproteins were separated by gradient sodium dodecyl sulphate gel electrophoresis (SDS-PAGE), electroblotted onto nitrocellulose membrane and probed with biotinylated lectins of characterised sugar specificities. The binding patterns of lectins from Maclura pomifera (MPA) and Arachis hypogaea (PNA) indicated that many parotid glycoproteins have sialylated O-linked glycans and that sialylation is not affected by disease. Binding by lectins from Ricinus communis (RCA-1), Limax flavus (LFA), Lotus tetragonolobus (LTA) and Ulex europaeus (UEA-1) appeared unaltered in secondary Sjögren's syndrome, suggesting no obvious change in N-glycosylation of parotid glycoproteins. Variations in binding patterns of most lectins was attributable to subject-to-subject variations in recognised polymorphic proteins. Dolichos biflorus agglutinin (DBA) consistently showed increased binding to a 75 kDa (Mr) protein in salivas from patients with secondary Sjögren's syndrome. The binding protein was identified as lactoferrin but found not to contain N-acetylgalactosamine, the sugar to which DBA binds. Binding of DBA to lactoferrin was dependent upon its saturation with iron, modified SDS-PAGE under nonreducing conditions resolved iron-free and iron-saturated lactoferrins and demonstrated increased levels of the iron-saturated form in secondary Sjögren's syndrome. Lectin binding studies of purified lactoferrins from saliva, milk, and polymorphonuclear neutrophils suggested that raised levels of lactoferrin in saliva originate from salivary cells and not from inflammatory cells. These results suggest that DBA binding provides greater specificity as an indicator of salivary gland disease than measurement of lactoferrin levels alone.