Synthesis of water-soluble selenium reagents and their applications to protein chemistry

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For folding study of proteins with disulfide bonds (SS bonds), water soluble sulfur reagents are normally used. In this research project, new selenium compounds have been synthesized and applied to oxidative folding experiments of proteins. This study is based on a general chemical concept that selenium is more redox-acitive than sulfur.Two-types of water-soluble selenium reagents were synthesized. When one of the reagents was used for folding experiments, the reagent reacted with a reduced form of bovine pancreatic ribonuclease A rapidly (within 10 sec) and quantitatively to form protein SS bonds. To investigate details of the rapid processes, a quench-flow equipment was constructed. The kinetic experiments using the quench-flow equipment revealed that the reaction between the protein and the selenium reagent completes within 1 sec and also that the SS formation proceeds during 50 to 100 msec. The results suggested that the selenium reagent may be able to trap folding intermediates that are formed rapidly in the beginning of folding and are alive in a short period. Thus, the selenium reagents would be useful for oxidative folding study of proteins.In this research project, database analysis of weak interactions in PDB and ab initio molecular orbital calculations of single amino acids have been also carried out. S…O interactions were discovered in protein structures. Conformational preferences of a single amino acid in water were suggested to be important in the folding of a polypeptide chain to secondary structures.