Discovery of a Kojibiose Phosphorylase in Escherichia coli K‑12
journal contributionposted on 23.04.2018, 00:00 by Keya Mukherjee, Tamari Narindoshvili, Frank M. Raushel
The substrate profiles for three uncharacterized enzymes (YcjM, YcjT, and YcjU) that are expressed from a cluster of 12 genes (ycjM-W and ompG) of unknown function in Escherichia coli K-12 were determined. Through a comprehensive bioinformatic and steady-state kinetic analysis, the catalytic function of YcjT was determined to be kojibiose phosphorylase. In the presence of saturating phosphate and kojibiose (α-(1,2)-d-glucose-d-glucose), this enzyme catalyzes the formation of d-glucose and β-d-glucose-1-phosphate (kcat = 1.1 s–1, Km = 1.05 mM, and kcat/Km = 1.12 × 103 M–1 s–1). Additionally, it was also shown that in the presence of β-d-glucose-1-phosphate, YcjT can catalyze the formation of other disaccharides using 1,5-anhydro-d-glucitol, l-sorbose, d-sorbitol, or l-iditol as a substitute for d-glucose. Kojibiose is a component of cell wall lipoteichoic acids in Gram-positive bacteria and is of interest as a potential low-calorie sweetener and prebiotic. YcjU was determined to be a β-phosphoglucomutase that catalyzes the isomerization of β-d-glucose-1-phosphate (kcat = 21 s–1, Km = 18 μM, and kcat/Km = 1.1 × 106 M–1 s–1) to d-glucose-6-phosphate. YcjU was also shown to exhibit catalytic activity with β-d-allose-1-phosphate, β-d-mannose-1-phosphate, and β-d-galactose-1-phosphate. YcjM catalyzes the phosphorolysis of α-(1,2)-d-glucose-d-glycerate with a kcat = 2.1 s–1, Km = 69 μM, and kcat/Km = 3.1 × 104 M–1 s–1.