| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1991: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1990: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
To investigate the structural and functional properties of lysozyme, various mutant enzymes were constructed by protein engineering. Lysozyme mutants deamidated at positions 103 (NlO3D) and 106 (NlO6D), cleaved salt linkage between Iys 13 and leu 129 (K13D), and deleted SS bond between positions 96 and 74 (C96/74A) were prepared. The wild-type and mutant lysozymes were expressed in Saccharomyces cerevisiae and purified from the cultivation medium in two steps by cation exchange chromatography on CM-Toyopearl. The lytic activities of each mutant lysozymes were almost the same as that of wild lysozyme, although the optimal pH of activity was slightly shifted to lower pH by the deamidation. -The Gibbs free energy changes of unfolding(DELTAG)at 20ﾟC for N103D and N106D were almost the same as that of wild-type. On the other hand, the structural flexibility of lysozymes, estimated by protease digestion, was significantly increased by the deamidation. The surface functional properties of deamidated lysozymes were considerably enhanced, compared to those of wild-type lysozyme. These results suggest that structural flexibility is an important governing factor in surface functional properties of proteins, regardless of their structural stability. On the other hand, DELTA G of mutant K13D and C96/74A was much lower than that of wild-type lysozyme, suggesting their unstable structure. These mutants had better surface properties than deamidated lysozymes. Thus, protein stability seems to be more effective factor than its flexibility for the surface functional properlies of proteins.
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