A highly efficient galactokinase from Bifidobacterium infantis with broad substrate specificity

Galactokinase (GalK), particularly GalK from Escherichia coli, has been widely employed for the synthesis of sugar-1-phosphates. In this study, a GalK from Bifidobacterium infantis ATCC 15697 (BiGalK) was cloned and over-expressed with a yield of over 80 mg/L cell cultures. The kcat/Km value of recombinant BiGalK toward galactose (164 s−1 mM−1) is 296 times higher than that of GalK from E. coli, indicating that BiGalK is much more efficient in the phosphorylation of galactose. The enzyme also exhibits activity toward galacturonic acid, which has never been observed on other wild type GalKs. Further activity assays showed that BiGalK has broad substrate specificity toward both sugars and phosphate donors. These features make BiGalK an attractive candidate for the large scale preparation of galactose-1-phosphate and derivatives.

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► GalK from Bifidobacterium infantis was expressed over 80 mg/L cell cultures.
► The enzyme exhibits high activity toward galactose with a kcat/Km of 164 s−1 mM−1.
► The wild type enzyme could phosphorylate galacturonic acid.
► The enzyme utilizes a variety of nucleoside triphosphates as phosphate donors.