Relatively little is known about the mechanisms of regulation of intracellular transport and sorting of salivary proteins, and these deficiencies have been recognized recently in a program announcement from the NIDR. The research that is proposed addresses the mechanisms of sorting of parotid proline-rich proteins (PRPs). Current studies that are being conducted by expressing PRPs in pituitary AtT-20 cells have shown that intracellular transport and storage of PRPs in secretion granules appears to involve a hierarchy of intermolecular interactions. The evidence obtained indicates that both small N-terminal oligopeptide domains and post-transnational modifications, particularly sulfated glycosaminoglycan chains are essential elements in these processes and promote efficient sorting of various PRPs in this experimental system. Three of the specific aims that are now outlined will examine the structural elements that are involved in sorting of PRPS in AtT-20 cells in much more detail and will emphasize an approach involving coexpression of different PRPs.
A fourth aim will extend these studies to other salivary proteins, particularly amylase and leucine-rich parotid secretory protein. The remaining three aims are devoted to examining sorting in parotid. Transgenic mouse lines expressing epitope-tagged PRPs (and related mutants) will be developed collaboratively and use to study sorting in parotid acinar cells and to explore the structural basis of binding of PRPs to parotid secretion granule membranes. Also sedimentation analysis will be performed in seeking direct evidence for aggregation of PRPs and correlation of these interactions being studied involve a class of proteins that is thought to have a central role in regulating the physicochemical properties and microbial environment at enamel surfaces. Thus an important long range goal is to investigate the relationship of intermolecular interactions involved in secretory sorting to maintenance of oral physiology.
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