AbstractsBiology & Animal Science

New insights into molecular recognition of epitopes related to MUC1 human mucin by lectins

by David Madariaga Merino

Institution: Universidad de La Rioja
Year: 2015
Record ID: 1124251
Full text PDF: http://dialnet.unirioja.es/servlet/oaites?codigo=44390


Tn antigen ( -O-GalNAc-Ser/Thr) is one of the most specific human tumorassociated structures. This motif is implicated in HIV infection and it is expressed early in tumor cells. It has been observed that there is a direct correlation between carcinoma aggressiveness and the density of this antigen. For this reason, Tn determinant is a convenient cancer biomarker. Mucin-like glycopeptides and glycoproteins, in particular MUC1, incorporate this structure in their sequence. While in normal cells this O-glycosylated protein carries complex oligosaccharides, in cancer cells, MUC1 expression is increased and its glycans are short and poorly branched. Therefore, Tn antigen is now exposed to the immune system generating an immunological response. From a structural point of view, Tn antigen is referred to Nacetylgalactosamine (GalNAc) -O-linked to serine (Ser) or threonine (Thr), not discriminating the amino acid to which GalNAc is linked. However, in this Thesis, we have synthesized different representative MUC1 epitopes bearing Ser and Thr in their structure and we have detected differences between these two amino acids in terms of affinity to lectins. As a result, it is important to mention specifically the underlying amino acid in Tn antigen. We have also analyzed the role of flanking amino acids of Tn antigen in the peptide chain, getting surprising results in terms of affinity to lectins. In addition, we have obtained an X-ray structure by the first time of soybean agglutinin (SBA) lectin linked to a MUC1-derived glycopeptide. All these results may have important implications for better understanding the glycopeptide-lectin interactions and may contribute to engineer new binding sites, allowing the design of novel glycosensors for Tn antigen detection in tumor cells. El antígeno Tn ( -O-GalNAc-Ser/Thr) es una de las estructuras asociadas a tumores más específicas en humanos. Esta molécula está implicada en la infección del VIH y en su expresión temprana en células tumorales. También se ha observado una relación directa entre la agresividad de un carcinoma y la concentración de dicho antígeno. Por ello, el antígeno Tn está considerado como un importante biomarcador del cáncer. Los glicopéptidos y glicoproteínas tipo mucina, en particular la mucina humana MUC1, incorporan en su estructura el antígeno Tn. Mientras que en las células sanas esta O-glicoproteína de membrana tiene oligosacáridos complejos, en células cancerosas, la expresión de MUC1 aumenta y sus glicanos son cortos y poco ramificados. Esto hace que el antígeno Tn quede expuesto al sistema inmune generando una respuesta inmunológica. Desde el punto de vista estructural, el antígeno Tn está formado por Nacetilgalactosamina (GalNAc) unida mediante un enlace -O-gliosídico a serina (Ser) o treonina (Thr), sin especificar a qué aminoácido se une el GalNAc. Sin embargo, en esta tesis hemos sintetizado diferentes epítopos representativos de MUC1 que incorporan Ser y Thr en su estructura. Hemos analizado las interacciones que ocurren en el reconocimiento de…