Show summary
Lectins, sugar binding proteins of non-immune origin, are one of the many weapons used by plants and fungi to defend themselves against potential predators and parasites. This role is often fulfilled by the presence of an additional domain or subunit with catalytic function.
The Marasmius oreades agglutinin (MOA) is a Gal-3Gal specific lectin extracted from the fruiting body of the Marasmius oreades mushroom. Parenterally administered MOA triggers a systemic effect in mice, which closely resembles the symptoms of the shiga toxin-induced hemolytic uremic syndrome (Stx-HUS) in humans. The structure of the MOA homodimer in complex with calcium, solved by X-ray crystallography [1], suggests an enzymatic function associated to the C-terminal dimerization domain, experimentally confirmed to be associated with proteolytic activity [2].
The enzymatically active domain of MOA shows an / hydrolase fold, bearing a structural resemblance to the enzymes of the papain-like cysteine peptidase family (clan CA). A notable feature in MOA is the conservation of two key residues of the catalytic triad (Cys215 and His257), while the third residue is substituted by an amino acid with similar properties (Glu274 in place of Asp). Here, we present further evidence, including crystallographic data, pointing to a key role of these residues for catalysis.
[1] Grahn, E.M., Winter, H.C., Tateno, H., Goldstein, I.J., Krengel, U., (2009). J. Mol.. Biol., 390, 457–466
[2] Cordara, G., Egge-Jacobsen, W., Johansen, H.T., Winter, H.C., Goldstein, I.J., Sandvig, K., Krengel, U. (2011). Biochem. Biophys. Res. Commun., 408, 405-410.