The Sclerotinia sclerotiorum agglutinin represents a novel family of fungal lectins remotely related to the Clostridium botulinum non-toxin haemagglutinin HA33/A.
Previous studies indicated that sclerotes of the phytopathogenic Ascomycete Sclerotinia sclerotiorum contain a lectin that based on its molecular structure, specificity and N-terminal amino acid sequence could not be classified yet into any lectin family. Using a combination of molecular cloning, frontal affinity chromatography and molecular modelling the identity of the S. sclerotiorum agglutinin (SSA) was analyzed. Molecular cloning demonstrated that SSA shares no sequence similarity with any known fungal lectin or protein. The lectin is synthesized as a 153 amino acid polypeptide without signal peptide and undergoes apart from the removal of the N-terminal methionine no further processing. Frontal affinity chromatography revealed that the binding site of SSA primarily accommodates a non-reducing terminal GalNAc with a preference for the alpha- over the beta-anomer. SSA also strongly interacts with both glycolipid type glycans with terminal non-reducing Gal or GalNAc and galactosylated N-glycans. SSA shares a residual sequence similarity with part of the non-toxin haemagglutinin HA33/A from Clostridium botulinum. Molecular modeling using the three-dimensional structure of HA33/A as a template indicated that SSA can fold into a similar beta-trefoil domain. Though these results should be interpreted with care it is tempting to speculate that the Sclerotiniaceae lectins thus appear to be structurally related to the ricin-B superfamily. All evidence suggests that SSA represents a novel family of fungal lectins with a unique sequence and sugar-binding properties. Taking into account that orthologues of SSA are fairly common within the family Sclerotiniaceae but could not be identified in any other fungal species one can reasonably conclude that SSA-type lectins are confined to a small taxonomic group of the Ascomycota.
Van Damme
Els J M
EJ
Department of Molecular Biotechnology, Lab. Biochemistry and Glycobiology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium. ElsJM.VanDamme@UGent.be
Nakamura-Tsuruta
Sachiko
S
Hirabayashi
Jun
J
Rougé
Pierre
P
Peumans
Willy J
WJ
D000373:Agglutinins / Q000737:chemistry* / Q000235:genetics; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000235:genetics / Q000276:immunology*; D001483:Base Sequence; D002240:Carbohydrate Sequence; D003001:Cloning, Molecular; D003014:Clostridium botulinum / Q000235:genetics / Q000276:immunology*; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics; D006388:Hemagglutinins / Q000737:chemistry* / Q000235:genetics; D057927:Hydrophobic and Hydrophilic Interactions; D037102:Lectins / Q000737:chemistry* / Q000145:classification / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012276:Ricin / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
D000373:Agglutinins; D004271:DNA, Fungal; D005656:Fungal Proteins; D006388:Hemagglutinins; D037102:Lectins; D012276:Ricin