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β-Galactosidase is widely used for hydrolysis of whey lactose. However, galactose inhibition has acted as a major constraint on the catalytic process. Thus, it is sensible to improve upon this defect in β-galactosidase through protein modification. To reduce the galactose inhibition of Aspergillus candidus β-galactosidase (LACB), four amino acid positions were selected for mutation based on their molecular bindings with galactose. Four mutant libraries (Tyr96, Asn140, Glu142, and Tyr364) of the LACB were constructed using site-directed mutagenesis. Among all of the mutants, Y364F was superior to the wild-type enzyme. The Y364F mutant has a galactose inhibition constant (K i) of 282 mM, 15.7-fold greater than that of the wild-type enzyme (K i = 18 mM). When 18 mg/ml galactose was added, the activity of the wild-type enzyme fell to 57% of its initial activity, whereas Y364F activity was maintained at over 90% of its initial activity. The wild-type enzyme hydrolyzed 78% of the initial lactose (240 mg/ml) after 48 h, while the Y364F mutant had a hydrolysis rate greater than 90%. The β-galactosidase Y364F mutant with reduced galactose inhibition may have greater potential applications in whey treatment compared to wild-type LACB.
Pubmed ID: 30333954
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Database that describes the families of structurally-related catalytic and carbohydrate-binding modules (or functional domains) of enzymes that degrade, modify, or create glycosidic bonds. This specialist database is dedicated to the display and analysis of genomic, structural and biochemical information on Carbohydrate-Active Enzymes (CAZymes). CAZy data are accessible either by browsing sequence-based families or by browsing the content of genomes in carbohydrate-active enzymes. New genomes are added regularly shortly after they appear in the daily releases of GenBank. New families are created based on published evidence for the activity of at least one member of the family and all families are regularly updated, both in content and in description. An original aspect of the CAZy database is its attempt to cover all carbohydrate-active enzymes across organisms and across subfields of glycosciences. One can search for CAZY Family pages using the Protein Accession (Genpept Accession, Uniprot Accession or PDB ID), Cazy family name or EC number. In addition, genomes can be searched using the NCBI TaxID. This search can be complemented by Google-based searches on the CAZy site.
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