Use of lectin-probes for correlative histochemical and biochemical assessments of the glycosylation patterns of secretory proteins, including kallikreins, in salivary glands and saliva

Abstract

Labelled lectins were used as probes to study the glycosylation and secretion of submandibular glycoproteins not only in sections of fixed glands but also in glandular extracts and in nerve-induced saliva, after electrophoretic separations and immobilization in nitrocellulose membranes. In cats the glycoproteins in sympathetic saliva differed considerably from those in parasympathetic saliva. In sympathetic saliva they were found to originate mainly from striated ducts, to some extent from demilunar cells and to a small extent from acinar cells, whereas in parasympathetic saliva they arose mainly from acinar-cells añd demilunes and only to a small extent from striated ducts. In rat submandibular glands sympathetic stimulation caused extensive depletion of lectin stainable granules from granular tubules. Corresponding strong binding occurred with the same lectins to constituents in saliva that ran between 25 and 35 kD on SDS gel electrophoresis and were shown to contain tissue kallikreins. Their binding patterns suggested that individual kallikreins from the same gland may be glycosylated in different ways. This possibility was tested on five different kallikreins after separation from submandibular extracts by isoelectric focussing. Lectin bindings on slot blot preparations of these kallikreins were tested before and after N-glycosidase F, sialidase or endo-a-Nacetylgalactosaminidase digestions. Results showed that, despite their close genetic and structural similarities, the kallikreins are in fact differently sialylated and fucosylated and the novel finding that some contain Oglycosidically linked side chains as well as the anticipated N-glycosidically linked side chains was revealed. Thus, correlative histochemical and biochemical Offprint requests to: Professor J.R. Garrett, Secretory and Soft Tissue Research Unit, Department of Oral Pathology, The Rayne Institute, KCSMD, 123 Coldharbour Lane, London, SE5 9NU, England assessments of bindings with lectin probes has provided important new information about differences in the glycosylation pattems of individual glycoproteins stored within the same secretory granules.