Identification of a High-Molecular-Weight Glycoconjugate from a Uruguayan Plant that Binds to the Tumor-Associated Tn Antigen

Abstract

The Tn determinant (GalNAc-O.-Ser/Thr), one of the most specific human carcinoma–associated structures, can be identified using both monoclonal antibodies and lectins. In this work we have explored, for the first time, the presence of Tn-binding proteins in aqueous extracts of plants collected in Uruguay. A total of 21 extracts from plants belonging to 12 Phanerogam families were screened by an ELISA assay (competitive inhibition of anti-Tn antibody binding) and by hemagglutination (HAG) activity. Five of the extracts displayed binding to Tn residues, although only those extracts prepared from fruit and leaf from Myrsine coriacea. (Sw.) R. Br. ex Roem & Schult caused total inhibition of the binding activity of anti-Tn MAb 83D4. Considering that Myrsine coriacea. extracts did not display HAG activity against several types of normal red blood cells, we characterized the material with Tn-binding activity from these extracts. We purified this material from Myrsine coriacea. leaf extracts using perchloric acid treatment followed by affinity chromatography and reverse-phase high performance liquid chromatography (HPLC), conserving its Tn-binding activity. We found a high-molecular-weight glycoconjugate that has an apparent molecular mass of approximately 670 kDa, as judged by SDS-PAGE.

Keywords:

• High-molecular-weight glycoconjugates
• plant lectins
• Tn antigen
• Tn-binding proteins
• Uruguayan plants