PROTEIN ENGINEERING OF HUMAN-LYSOZYME

A gene encoding human-lysozyme was chemically synthesized and expressed both in E. coli and S. cerevisiae. The gene product expressed in E.coli formed insoluble material and had no enzymatic activity . For the expression in S. cerevisiae a signal sequence of chicken-lysozyme was attached. Prehuman-lysozyme expressed in yeast was properly processed and secreted outside the cell. Amino acid residues of catalytic and recognition sites (Glu35, Asp53, Tyr63, Trp64, Trp109) of human-lysozyme were changed by site specific mutagenesis and their influence to the enzymatic activity was examined. The surface charge of the enzyme has great effects on enzymatic activity to charged substrates. By increasing or decreasing the surface charge of human-lysozyme the optimum ionic strength or PH was shifted