However, when double mutants were examined there was a complete loss of hydrolysis, but binding to PSA still occured. Single mutations of those residues reduced the level of activity, but not enough to mark the residues as absolutely required. Instead, three conserved amino acids (Arg596, Arg647 and Glu581) were observed that contribute to endosialidase activity. įrom the crystal structure of the GH-58 enzyme it was noted that the normal catalyic residues found in exo-sialidases were not present. Direct 1H-NMR analysis of the hydrolysis of trifluoromethylumbelliferyl sialotrioside revealed that endoNF affects catalysis with an inverting mechanism. Measurement of k cat/K m at a series of pH values revealed a dependence on a single protonated group of pK a 5. Using synthetic trifluoromethylumbelliferyl oligosialoside substrates kinetic parameters for hydrolysis at a single cleavage site were determined. The recently determined structure of an endo-sialidase derived from bacteriophage K1F (endoNF) revealed the active site to lack a number of the residues that are conserved in other sialidases, implying a new, endo-sialidase-specific catalytic mechanism. coli capsule type have been described which have tailspike enzymes that degrade the capuslar material įamily 58 endo-sialidases are specific for polysialic acid and form a unique family of endo-acting sialidases, all others previously reported being exo-acting. A range of bacteriophages specific to this E. coli K1, is poly-α-2,8-sialic acid and protects the bacterium from the host immune system, but it also acts as an anchor point for bacteriophage infection. Glycoside hydrolases of family 58 are endo- N-acetylneuraminidases (also termed endo-sialidases).
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