About the Lectin

A lectin from the fruiting body of the polypore
mushroom Polyporus squamosus with an extended carbohydrate
binding site that exhibits high specificity and affinity for non
reducing, terminal Neu5Acα2,6Galβ1,4GlcNAc residues of N-linked
glycans ¹ ; it does not recognize α2,3-linked sialic acid.
Importantly, it does not recognize the Neu5Acα2,6GalNAc
moiety present in ovine submaxillary mucin in contrast to
the S. nigra agglutinin which requires only the disaccharide
group ² . This indicates the necessity for three structural
features for interaction with PSL. The lectin has been cloned
and the recombinant lectin is available as a homogenous
white powder. It is also available in its fluorescein- and
biotinylated-forms as well as bound to agarose for use in
affinity chromatography.

The native lectin, designated P. squamosus agglutinin,
is composed of two identical 28kDa subunits associated by
noncovalent bonds. P. squamosus agglutinin agglutinated
human A, B, and O and rabbit red blood cells but precipitated
only with human α₂– macroglobulin, of many glycoproteins
and polysaccharides tested. ¹ Although the P. squamosus lectin
binds β-D-galactosides, it has an extended carbohydratecombining
site that exhibits highest specificity and affinity
toward nonreducing terminal Neu5Acα2,6Galβ1,4Glc/
GlcNAc(6’-sialylated type II chain) of N-glycans (2000-fold
stronger than toward galactose). The strict specificity of the
lectin for α2,6-linked sialic acid renders this lectin a valuable
tool for glycobiological studies in biomedical and cancer
research. ¹

cDNA cloning revealed that P. squamosus lectin
contains a ricin B chain-like (QXW)3 domain at its N-terminus
that is composed of three homologous subdomains (α, β, and
γ). A recombinant lectin was expressed in Escherichia coli as a
fully active, soluble form. It agglutinated rabbit erythrocytes
and showed greatest affinity for Neu5Acα2,6Galβ1,4GlcNAc,
but not the sialyl α2,3- linked isomer. In investigations of
the structure-function relationship of PSL, a monomeric Cterminal
deletion mutant lacking 40% of the lectin’s molecular
weight retained sugar-binding activity, indicating that the
carbohydrate-binding sites are situated in the N-terminal
portionof the lectin, whereas the C-terminal portion possibly
functions in oligomerization and structural stabilization.
The EY Lectin is recombinantly-expressed and is a valuable
reagent for the detection of Neu5Acα2,6Galβ1,4GlcNAc
sequence of asparagine-linked glycans. ³

REFERENCES

1. Mo, H. et al. (2000) J. Biol. Chem. 275:10623-10629.
2. Toma, V. et al. (2001) Histochemistry 116: 183-193.
3. Tateno, H. , Winter, H., et al. (2004) Biochem J. 382 (667-675)