Leech sialidase

A similar situation to that with the lytic transglycosylases occurs with a leech sialidase (sialidase L), which gives 2,7-anhydro-A-acetylneuraminic acid, despite being in GH 33 like all other non-viral sialidases and transialidases. This enzyme binds a C-glycoside substrate-analogue (aNeuNAc-CH2-CH=CH2) and product in the conformation. The conformation of glycosyl-enzyme... 

Interestingly, the leech sialidase resulting in Neu2,7an5Ac also belongs to this family, since the consensus repeat S-X-D-X-G-X-T-W was found in tryptic peptides of this enzyme [61]. 

Endosialidases are not unique among sialidases in combining a p-propeller with other structures. Many other sialidases contain additional domains like p-barrels, jelly rolls, or immunoglobulin modules [116] which are placed N-terminally, C-terminally, or even inserted into the p-propeller. N-terminal lectin-like domains have been identified in leech sialidase L [117] and Vibrio cholerae sialidase [118]. Interestingly, in the V. cholerae sialidase a second p-structure domain is inserted... 

Kinetic evidence based uptm seccMidaiy deoterium isotope ects has indicaied that a sialidase isolated firom a leech cleaves the glycosidic link with the pyranosc ring adopting a normally disfavoured conformation. ... 

In addition to the common exo-a-sialidases (EC 3.2.1.18 Cabezas, 1991), a rare enzyme has been found, so far only in the leech (Li et al., 1993), yielding 2,7-anhydro-Neu5Ac as its reaction product. This compound may also be a product of an as yet unknown microbial sialidase, since it was found in human cerumen (Suzuki et al., 1985). 

Sialidase activity has been detected in certain invertebrate species. A recent study has demonstrated that the leech Macrobdella decora contains not only an ordinary sialidase, but also a novel sialidase which releases 2,7-anhydro-a-A-acetylneuraminic acid from various sialoglycoconjugates (Li et al., 1990). The purified enzyme has a molecular mass of 84 kDa and shows strict specificity for the a2-3 linkage in Neu5AcLac and gangliosides the enzyme does not cleave the a2-6 and a2-8 linkages (Chou et al., 1992). The mechanism of action of this enzyme is unknown. 

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