Glycoside Hydrolase Family 58

• Author: ^^^Warren Wakarchuk^^^
• Responsible Curator: ^^^Warren Wakarchuk^^^

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Glycoside Hydrolase Family GH58
Clan	none
Mechanism	inverting
Active site residues	known/not known
CAZy DB link
http://www.cazy.org/fam/GH58.html

Substrate specificities

endo-N-acetylneuraminidase or endo-sialidase

The capsular coat surrounding E. coli K1, protects the bacterium from degradation by the host immune system, but it also acts as an anchor point for bacteriophage infection. The capsular material for K1 is poly-a-2,8-sialic acid and a range of bacteriophages specific to this E. coli capsule type have been described which have tailspike enzymes that degrade the capuslar material [1, 2, 3]

Kinetics and Mechanism

This enzyme is specific for polysialic acid and is one of a unique family of endo-sialidases, all others previously reported being exo-sialidases. The recently determined structure of an endosialidase derived from bacteriophage K1F (endoNF)[3] revealed the active site to lack a number of the residues that are conserved in other sialidases, implying a new, endosialidase-specific catalytic mechanism. Using synthetic trifluoromethylumbelliferyl oligosialoside substrates kinetic parameters for hydrolysis at a single cleavage site were determined. Measurement of k_cat/K_m at a series of pH values revealed a dependence on a single protonated group of pKa 5. Direct ¹H-NMR analysis of the hydrolysis of trifluoromethylumbelliferyl sialotrioside revealed that endoNF is an inverting sialidase [4].

Catalytic Residues

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Three-dimensional structures

The structure for the K1F tailspike enzyme has been solved by Stummeyer et al. [5]. The protein structure is similar to other phage tailspike endo-hydrolases in that it is a an extended molecule that is trimeric.

Family Firsts

First sterochemistry determination

The stereochemical outcome of this reaction was determined in the Withers laboratory at UBC using synthetic substrates with a trifluoromethyl-umbelliferol fluorophore [3]. This determination showed that unlike all other known sialidases, the endo-sialidase uses an inverting mechanism.

First catalytic nucleophile identification

Cite some reference here, with a short (1-2 sentence) explanation [6].

First general acid/base residue identification

Cite some reference here, with a short (1-2 sentence) explanation [7].

First 3-D structure

The first structure determination was performed with the K1F protein [3].

References

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4. Stummeyer K, Dickmanns A, Mühlenhoff M, Gerardy-Schahn R, and Ficner R. (2005). Crystal structure of the polysialic acid-degrading endosialidase of bacteriophage K1F. Nat Struct Mol Biol. 2005;12(1):90-6. DOI:10.1038/nsmb874 |
5. Morley TJ, Willis LM, Whitfield C, Wakarchuk WW, and Withers SG. (2009). A new sialidase mechanism: bacteriophage K1F endo-sialidase is an inverting glycosidase. J Biol Chem. 2009;284(26):17404-10. DOI:10.1074/jbc.M109.003970 |