About the Lectin

Eel serum contains an anti-H specific lectin which differs in potency depending on the purification technique and the electrophoretic characteristics of the final product. Uhlenbruck, et al ¹ reported the presence of two different anti-galactan lectins in the serum of Anguilla anguilla. Futhermore, Gercken and Renwrantz ² isolated a mannam-binding lectin with hemagglutinating properties in eel serum. One is composed of two subunits linked by a disulfide bridge. The other is a C-reactive protein (CRP) analog which also appears to have lectin-like activity. Other researchers have reported a variety of different molecular weights for the purified fucolectin. Bezkorovainy, et al ³ reported a MW=123,000 composed of three non-covalently bound subunits. Horejsi, et al ⁴ obtained a MW=50,000 by gel filtration but a much larger value as determined by the sedimentation coefficient. Other analytical techniques led this group to conclude that the lectin is composed of two subunits with an aggregate molecular weight of 44,000 Da. Re-analysis by Kelly ⁴ of the purified lectin gave two peaks of MW=51,000 and 78,000 Da. Further analysis indicated that the lectin is a dimer of aggregate MW=38,000. EY Laboratories supplies a product that exhibits the same heterogeneous composition described by many researchers. There are similarities between the fucose specific lectins from Anguilla anguilla, Lotus tetragonolobus, and Ulex europaeus I. In comparison to L-fucose itself, methyl &#945-L-fucose is a much stronger inhibitor of all three lectins. However, only AAA and Lotus are inhibited if the methyl substitution occurs at C2 or C3. Of special interest is the finding that AAA is also inhibited by methyl substituted D-fucose. In view of the structural similarities between fucose and galactose, it is perhaps not surprising that 3-O-methylgalactose is also an inhibitor of lectin activity. In direct binding sites, AAA bound H- and Le oligosaccharides with terminal Fucα1,2 and subterminal Fucα1,4 linkages equally well, whereas UEA-I exhibited a strong preference for the Fucα1,2 structure, as on Leb, but not Lea structures ⁶ . AAA apparently has a small carbohydrate binding site since complex carbohydrates do not exhibit higher inhibitory potency than the methyl substituted monosaccharide, in contrast with the majority of other lectins which generally are more reactive with complex carbohydrates than with a monosaccharide. Immobilized AAA has been used to purify the glycocalyx covering of cercariae of Schisosoma parasites, which is a peptidoglycan whose carbohydrate is composed of 40% fucose ⁷ .

REFERENCES

1. Uhlenbruck, G., et al. (1982). Immunobiol. 163: 36-47.
2. Gercken, J. and Renwrantz, L. (1994) Comp. Biochem. Physiol.: Biochem. Mol. Biol. 108 : 449-461.
3. Bezkorovainy, A., et al. (1971). Biochemistry.10: 3761-3764.
4. Horejsi, V. and Kocourek, J. (1978). Biochem. Biophys. Acta. 538: 299-315.
5. Kelly, C. (1984). Biochem. J. 220 : 221-226.
6. Baldus, S. E., et al. (1996) Glycoconj. J. 13 : 585-590.
7. Xu, X. (1994) Exp. Parasitol. 79 : 399-409.