Lactobacillal ß-galactosidases: structure and function

Galacto-oligosaccharides (GOS), which are the products of transgalactosylation reactions catalyzed by ß-galactosidases when using lactose as the substrate, are of special interest to human nutrition because of the presence of structurally related oligosaccharides together with different complex structures in human breast milk. Recently, a number of studies have focused on the use of the genus Lactobacillus for the production and characterisation of ß- galactosidases. It is anticipated that GOS produced by these ß-galactosidases will have better selectivity for the growth and metabolic activity of this bacterial genus in the gut, and thus will lead to improved prebiotic effects. Despite numerous studies on the gene clusters involved in lactose utilization by these bacteria and their biochemical properties pertaining to their ability to produce GOS in biocatalytic processes, the functional roles of the key residues in the active sites of the ß-galactosidases from this important bacterial group have not been studied. This research project aims to identify potential residues involved in transgalactosylation activity of lactobacillal ß-galactosidases. Structure-function relationships of lactobacillal ß-galactosidases regarding GOS product linkage specificity will allow rational design of mutations of ß-galactosidases to produce specific mixtures of GOS structures. Hence, different GOS product specificities and yields are expected.