The mammalian respiratory tract is protected by mucus secretions which are synthesized in the surface epithelium and in submucosal acinotubular glands in the trachea. The surface epithelium of the tracheobronchial airway is coated with mucus which is constantly removed by the mucociliary transport system. The viscoelastic properties of mucus secretions, the clearance off particulate matter, the maintenance of water balance and the rate of removal of mucus are dependent on the amount and composition of mucin glycoproteins in mucus. The rate of synthesis and secretion of mucin glycoproteins on to the epithelial surface, and the transport of mucus from the surface play a fundamental role in the maintenance of the sterility and stability of the trachea mucus membrane. The carbohydrate chains in mucin glycoproteins play an important role in these biological functions. The objective of the proposed research is to define the mechanisms which regulate the composition and rate of synthesis off O-ser (thr) linked oligosaccharide chains in mucin glycoproteins. The composition and structure of these oligosaccharide chains are ultimately determined by the activity of a series of specific glycosyltransferases. The mechanisms which regulate the final number and structure of different oligosaccharide chains in mucin glycoproteins have not yet been identified. The present proposal describes studies on the glycosyltransferases which are involved in the synthesis of oligosaccharide chains, with a major emphasis on the branching and chain elongating enzymes.
The specific aims i nclude: 1) to continue studies on the purifications and characterization of glycosyltransferases in trachea epithelium which synthesize O-ser (thr) linked oligosaccharide chains; 2) to complete structural studies on the oligosaccharide chains in swine trachea mucin glycoproteins and prepare well characterized homologus glycosyl acceptors to examine the kinetic properties of the purified glycosyl transferases. These studies may enable us to establish a pathway for the synthesis of the more complete chains; 3) to use a mucus-secreting epithelial cell system to examine the regulation of synthesis and secretion of mucin glycoproteins. The influence of various hormones and secretory stimuli on the rate of synthesis and composition of oligosaccharide chains in secreted mucin glycoproteins will be investigated. The data obtained in these studies will yield significant information on the properties of these transferases and the mechanisms involved in the regulation of mucin glycoprotein synthesis.
