ScrB (Cg2927) is a sucrose-6-phosphate hydrolase essential for sucrose utilization byCorynebacterium glutamicum

Abstract

Corynebacterium glutamicum can grow on a variety of carbohydrates from which glucose, fructose and sucrose are taken up and phosphorylated by the phosphoenolpyruvate-dependent phosphotransferase system (PTS). Here, we show that cg2927 (scrB) encodes sucrose-6-phosphate hydrolase. The purified His-tagged protein hydrolyzed sucrose-6-phosphate and sucrose, but not sucrose-6'-phosphate. The Km value for sucrose was 190 mM while the Km for sucrose-6-phosphate was much lower, 0.04 mM. Sucrose-6-phosphate hydrolase activity was stimulated by MgSO4 and fructose-6-phosphate and was inhibited by MnCl2, CaCl2, CuSO4 and ZnSO4. A scrB deletion mutant could not grow on sucrose as the sole carbon source. In addition, growth in the absence of scrB was severely decreased when sucrose was present in addition to glucose, fructose or acetate, suggesting that higher intracellular concentrations of sucrose-6-phosphate are toxic. Transcriptional start sites in the cg2929-cg2928-scrB-ptsS locus could be revealed upstream of cg2929 and upstream of the sucrose-specific PTS gene ptsS. Of these, only ptsS showed increased expression when grown in the presence of sucrose, which was due to control by the transcriptional regulator SugR. The sucrose-6-phosphate hydrolase activity, however, was increased two- to threefold during growth in fructose- or sucrose-containing media, regardless of the presence or absence of SugR.