Molecules found in human saliva have many protective functions critical to oral health. The protective qualities of saliva become evident in individuals with markedly decreased salivary flow (xerostomia or dry mouth). The long range goal of our research is to design and produce the individual and/or chimeric human salivary molecules with enhanced protective functions and to use these as prototypes for development of artificial salivas. An essential prerequisite for this goal is the complete understanding of the structure-function relationship of individual salivary molecules. The availability of mutants provides one of the most powerful ways to achieve this objective. The use of molecular biological techniques and recombinant DNA technology proposed in this application for the production the native, variant (mutant) and chimeric forms of proteins in the heterologous system (E coli) will allow us to study the salivary protein's structure and their function at the molecular level and permit a rational design of salivary substitutes. Recently, we have obtained recombinant clones encoding several types of salivary proteins which will enable us to carry out the proposed studies. Molecules that we will concentrate on are cystatins (cysteine proteinase inhibitors and anti-bacterial/viral agents) and histatins (anti-fungal, particularly anti-candidal and anti-bacterial agents), since they have key protective functions and are amongst the best characterized salivary molecules on a biochemical basis. Specifically, we propose to: 1)produce large amounts of biologically active cystatin and histatin in E coli expression system, 2) construct mutants of cystatin and histatin which will be used for mapping the structural domains and/or individual amino acid residues that are essential for the structural integrity and/or biological function of these proteins and 3) construct and produce various cystatin/histatin chimeric proteins with biological activities resembling or exceeding those of the parent proteins.