Melibiose

About: Melibiose is a research topic. Over the lifetime, 1002 publications have been published within this topic receiving 27300 citations. The topic is also known as: Melibiose.

Proteolytic mapping and substrate protection of the Escherichia coli melibiose permease.

Abstract: The topology and substrate-induced conformational change(s) of the Na+ (Li+ or H+)-melibiose cotransporter (MelB) of Escherichia coli were investigated by limited protease digestion. To facilitate these analyses, MelB was epitope-tagged both at its carboxyl-terminus and at its amino-terminus. Limited digestion with different proteases indicates that the cytoplasmic loops connecting transmembrane domains 4-5, 6-7, and 10-11 together with the carboxyl-terminus of MelB are exposed in the cytoplasm. In contrast, periplasmic loops are highly resistant to all the proteases examined, including nonspecific proteases such as proteinase K and thermolysin. The effect of Na+ or Li+ and/or melibiose on the rate of protease digestion of the cytoplasmic loops was also analyzed. The rate of protease digestion of loop 4-5 is specifically reduced, by approximately 3-fold, by the presence of Na+ or Li+. These results suggest that loop 4-5 is near or part of the cation binding site. Moreover, the presence of both melibiose and either Na+ or Li+ further reduced the rate of protease digestion of this loop 4-5 by up to 9-fold, although no protection from protease digestion was observed when melibiose was added alone. The increase in resistance to proteases observed in the presence of the cation alone or the cation plus melibiose suggests that the interaction of the two cosubstrate with MelB results in change(s) of MelB conformation.

A novel α-galactosidase from the thermophilic probiotic Bacillus coagulans with remarkable protease-resistance and high hydrolytic activity.

Abstract: A novel α-galactosidase of glycoside hydrolase family 36 was cloned from Bacillus coagulans, overexpressed in Escherichia coli, and characterized. The purified enzyme Aga-BC7050 was 85 kDa according to SDS-PAGE and 168 kDa according to gel filtration, indicating that its native structure is a dimer. With p-nitrophenyl-α-d- galactopyranoside (pNPGal) as the substrate, optimal temperature and pH were 55 °C and 6.0, respectively. At 60 °C for 30 min, it retained > 50% of its activity. It was stable at pH 5.0-10.0, and showed remarkable resistance to proteinase K, subtilisin A, α-chymotrypsin, and trypsin. Its activity was not inhibited by glucose, sucrose, xylose, or fructose, but was slightly inhibited at galactose concentrations up to 100 mM. Aga-BC7050 was highly active toward pNPGal, melibiose, raffinose, and stachyose. It completely hydrolyzed melibiose, raffinose, and stachyose in < 30 min. These characteristics suggest that Aga-BC7050 could be used in feed and food industries and sugar processing.

Nutritional requirements and simplified cultivation medium to study growth and energetics of a sourdough lactic acid bacterium Lactobacillus fermentum Ogi E1 during heterolactic fermentation of starch.

Abstract: Aims: Nutritional requirements of Lactobacillus fermentum Ogi El were studied in order to define a simplified fermentation medium. Methods and Results: When grown with MRS-medium in 21 bioreactors, a biphasic pattern of growth and metabolite production was observed. Study of nutritional requirements resulted in a simplified medium (SYAM) that allowed, under anaerobiosis, similar results to be obtained as in MRS medium, but without biphasic fermentation kinetics. The best substrates for both growth and amylase production were starch and maltose. Although melibiose, raffinose, fructose, sucrose and glucose also supported growth, lower amylase activity was observed. Conclusions: The physiology of the strain can be investigated with SYAM medium, using either starch or maltose as substrate. The strain also presented potential for a-galactoside fermentation. Significance and Impact of the Study: Lactobacillus fermentum was one of the dominant bacteria of African maize dough fermentations. Amylolytic strains with activity against other compounds (i.e. raffinose) suggested a potential to be used as starter for cereal fermentation. (Resume d'auteur)