About the Lectin

A novel lectin has been isolated and cloned from
the leaves of Glechoma hederacea (ground ivy), a typical
representative of the plant family Lamiaceae. Biochemical
analyses indicated that the G. hederacea agglutinin (Gleheda)
is a tetrameric protein consisting of four subunits pairwise
linked through an interchain disulphide bridge and exhibits
a preferential specificity towards N-acetylgalactosamine.
Cloning of the corresponding gene and molecular modeling
of the deduced sequence demonstrated that Gleheda shares
high sequence similarity with legume lectins and exhibits
the same overall fold and three-dimentional structure as the
classical legume lectins. The identification of a soluble and
active legume lectin ortholog in G. hederacea not only indicates
that the yet unclassified Lamiaceae lectins belong to the same
lectin family as the legume lectins, but also sheds a new light on
the specificity, physiological role and evolution of the classical
legume lectins. ¹

Screening of a population of wild plants revealed that
Gleheda accounts for more than one-third of the total leaf protein
in some clones, whereas it cannot be detected in other clones
growing in the same environment. Gleheda is predominantly
expressed in the leaves where it accumulates during early leaf
maturation. The lectin is not uniformly distributed over the
leaves but exhibits a unique localization pattern characterized
by an almost exclusive confinement to a single layer of
palisade parenchyma cells. Insect feeding trials demonstrated
that Gleheda is a potent insecticidal protein for larvae of the
Colorado potato beetle (Leptinotarsa decemlineata). Because
Gleheda is not cytotoxic, it is suggested that the insecticidal
activity is linked to the carbohydrate-binding specificity of the
lectin, which as could be demonstrated by agglutination assays
with different types of polyagglutinable human erythrocytes
is specifically directed against the Tn antigen structure (N-acetyl-galactosamine
O-linked to serine or threonine residues of
proteins). ²

REFERENCES

1. Wang, W., et al. (2002) Plant Journal. 33: 293-304
2. Wang W, Hause B, et al. Plant Physiol. 2003 Jul;132(3):1322-34.