The overall goal of this project is to understand the role of histatins, a family of histidine-rich proteins present in human parotid and submandibular secretions, in the non-immune oral defense system. This family consists of 3 major histatins, histatin 1, 3, and 5, which exhibit Mrs of 4929, 4063, and 3037, respectively, and at least 9 minor histatins which are formally derived from major histatins by proteolysis. They differ from other salivary proteins in that they exhibit both antifungal and antibacterial properties, are histidine-rich, are of small molecular weight, and contain both phosphorylated and non-phosphorylated species. One of the most frequent sites of initial candidal infection is the oral cavity and this can lead to systemic fungal dissemination. Over the past decade the incidence of documented fungal infections has increased and disseminated candidiasis has a poor prognosis and is a major cause of death in compromised patients. The investigation of histatins may lead to therapeutic modalities suited for oral and other application against both fungal and bacterial organisms.
The specific aims of this project are: 1. To characterize the functions of histatins by a) determining their functional domains using peptides obtained by solid phase synthesis and recombinant DNA technology and b) developing bioassays suited to characterize the bacteriocidal and bacteriostatic effects of histatins and synthetic peptides. 2. To elucidate the anticandidal mechanisms of histatins by a) characterizing the interactions of histatins with C. albicans at the morphological level using immunofluorescence light microscopy and immunogold electron microscopy, and b) identifying the subcellular site of histatin action in C. albicans at a biochemical level using radiolabeled histatins and synthetic peptides. 3. To gain information on the structural and evolutionary relationship of histatin genes by a) sequencing the genes for histatin 1 and 3, b) determining whether histatin 5 arises from a distinct mRNA using PCR methodology, and c) using Southern analysis of genomic DNAs from primates, rodents, and ungulates to ascertain the distribution of histatin genes. 4. To determine the physiological histatin levels in whole saliva and salivary secretions and the survival of histatins in the oral cavity by a)immunoquantitation of histatins using polyclonal and monoclonal antibody preparations in ELISAs and b) analysis of histatin fragmentation patterns by enzymes present in the oral cavity using HPLC and gas phase sequencing for the characterization of histatin fragments.
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