The specific aim of this project is to analyze the biosynthesis and function-structure relationships of polymophic variants of H-2 linked complement projects, C4, S1p, C2, and B. We plan to continue one of our long-term objectives, the genetics, regulation, function and structure of mouse C4 and S1p. This project will emphasize functional aspects of C4 and S1p, especially as function relates to structure in polymorphic variants, and the biosynthesis of C4 and S1p by short-term in vitro mouse peritoneal macrophage and hepatocyte cultures. The methodology primarily involves biosynthetic labeling of C4 and S1p with radioactive sugar and amino acid precursors, immunoprecipitation and subsequent analysis of the precipitated complex by SDS-PAGE. This modus operandi will also be applied to B since antibodies are available and to C2 when the antibodies are produced. Sensitive hemolytic assays are now available for C4, C2 and B and polymorphic variants are known for each component. In the previous four years, much has been learned about the genetic regulation and function-structure relationships of mouse C4. [An important observation, that the secreted form of mouse and human C4 is about 5000 daltons larger than the major form of C4 in plasma, will be analyzed in regards to the protease responsible for the cleavage and function of the peptide released. We now plan to extend these studies to S1p, B and C2 while continuing our work on C4.] We believe our studies on C4 biosynthesis will progress to the point that they will become an instructive model of the evolution and control of a mammalian protein. Through continued genetic, structural and functional characterizations of these products, we hope to gain better insights into the basis for their control by the major histocompatibility complex.
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