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Sialic acids are acidic sugars present mostly on vertebrate cell surfaces, which can be metabolized by bacteria and act as an inflammation signal. N-Acetylneuraminic acid, the most abundant sialic acid, can enter into Escherichia coli K12 through NanC, an N-acetylneuraminic acid-inducible outer-membrane channel. With its 215 residues, NanC belongs to the family of small monomeric KdgM-related porins. KdgM homologues are found in gammaproteobacteria, including major plant and human pathogens, and together they define a large family of putative acidic sugar/oligosaccharide transporters, which are as yet poorly characterized. Here, we present the first high-resolution structure of a KdgM family member. NanC folds into a 28-Å-high, 12-stranded β-barrel, resembling the β-domain of autotransporter NalP and defining an open pore with an average radius of 3.3 Å. The channel is lined by two strings of basic residues facing each other across the pore, a feature that appears largely conserved within the KdgM family and is likely to facilitate the diffusion of acidic oligosaccharides. 相似文献
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Dana Flodrová Soňa Garajová Anna Malovíková Danica Mislovičová Jiřina Omelková Eva Stratilová 《Biologia》2009,64(2):228-234
The main form of pectate hydrolases in the cell wall of parsley roots showed a unique substrate preference of a plant exopolygalacturonase
because it clearly preferred the substrates with degree of polymerization about 10. This form was separated from the others,
purified and characterized. Enzyme exhibited sharp pH optimum corresponding to pH 4.7, molecular mass 53.5 kDa, and isoelectric
point 5.3. It was stable at 50°C in 2-h assay and had optimum of temperature at 60°C (activation energy being 37.0 kJ/mol).
The interaction with concanavalin A indicated the glycosylation of enzyme. Substrates were cleaved from the non-reducing end. 相似文献
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