Lactose is a disaccharide composed of galactose and glucose which naturally exist only in the milk. β-galacto-sidase is one of the crucial industrial enzymes that hydrolyzes lactose. Kluyveromyces marxianus can grow ...Lactose is a disaccharide composed of galactose and glucose which naturally exist only in the milk. β-galacto-sidase is one of the crucial industrial enzymes that hydrolyzes lactose. Kluyveromyces marxianus can grow on lactose as the only source of carbon and energy allowing this species to use whey as a cheap source. So far, no structural and comprehensive study has been done on its GAL/LAC system. Therefore, in this study, the proteins involved in the GAL/LAC system of K. marxianus were identified, and their secondary and tertiary structures and functions were determined for the first time. Also, the GAL80 inhibitory gene was deleted from the chromosome of this species. Its effect on β-Galactosidase enzyme production and its expression was investigated, as well as the expression of other genes involved in the production system of this enzyme. Lac9 and Lac12 proteins do not have beta sheets in their structures, in the Gal1, Gal7, and Gal80 proteins, the amount of helix is more than beta sheets, while in the Gal10 protein, the amount of beta sheets is more. Also, in the Lac12 protein, 46% of the total protein comprises transmembrane helices. Gal7 and Gal80 form homodimers in the cell. We showed that by deletion of the GAL80 gene from K. marxianus chromosome, the expression of genes involved in the GAL system, including LAC4 (β-galactosidase), LAC12 (permease), LAC9 (transcriptional activator), GAL1 (galactokinase), GAL7 (transferase), and GAL10 (epimerase), and the production of β-galactosidase, increased significantly in the culture medium containing different sugars.展开更多
文摘Lactose is a disaccharide composed of galactose and glucose which naturally exist only in the milk. β-galacto-sidase is one of the crucial industrial enzymes that hydrolyzes lactose. Kluyveromyces marxianus can grow on lactose as the only source of carbon and energy allowing this species to use whey as a cheap source. So far, no structural and comprehensive study has been done on its GAL/LAC system. Therefore, in this study, the proteins involved in the GAL/LAC system of K. marxianus were identified, and their secondary and tertiary structures and functions were determined for the first time. Also, the GAL80 inhibitory gene was deleted from the chromosome of this species. Its effect on β-Galactosidase enzyme production and its expression was investigated, as well as the expression of other genes involved in the production system of this enzyme. Lac9 and Lac12 proteins do not have beta sheets in their structures, in the Gal1, Gal7, and Gal80 proteins, the amount of helix is more than beta sheets, while in the Gal10 protein, the amount of beta sheets is more. Also, in the Lac12 protein, 46% of the total protein comprises transmembrane helices. Gal7 and Gal80 form homodimers in the cell. We showed that by deletion of the GAL80 gene from K. marxianus chromosome, the expression of genes involved in the GAL system, including LAC4 (β-galactosidase), LAC12 (permease), LAC9 (transcriptional activator), GAL1 (galactokinase), GAL7 (transferase), and GAL10 (epimerase), and the production of β-galactosidase, increased significantly in the culture medium containing different sugars.
