Immunochemical Studies on the Combining Site of Tn-Specific Lectin Vicia villosa B4

• Main Author: 郭安靜
• Other Authors: 吳明道
• Format: Others
• Language: zh-TW
• Published: 1992
• Online Access: http://ndltd.ncl.edu.tw/handle/28906309407597376604

碩士 === 國立臺灣大學 === 醫事技術學研究所 === 80 === The combining site of B4 lectin isolated from Vicia villosa seeds was characterized by quantitative precipidn (QPA) and precipitin inhibidon assays (QPIA). Among glycoproteins and polysaccharides examined by QPA, human blood group A, B, H, Lea, Leb, and I/i active glycoproteins, purified from human ovarian cyst fluid, and rat sublingual glycoprotein, reacted poorly with B4 lecdn as all of the T n (GalNAcα1->Ser/Thr) determinants of these glycoproteins are masked by long oligosaccharide chains, blood group determinants and/or sialic acids. When the Tn sequences were uncovered by mild acid hydrolysis and/or Smith degradation of these glycoproteins, they reacted strongly and precipitated more than two-thirds of B4 lectin added. B4 reacted weakly with T, I/II containing glycoproteins such as active antifreeze glycoprotein, and pneumococcus type XIV polysaccharide. But, the mixture of A & 8 subunits reacted in an opposite profile, i.e. strongly with A1 active glycoproteins and weakly with their Smith degraded or mild acid hydrolyzed products. This indicates that the B4 lectin recognizes exclusively the Tn epitope and that the carbohydrate affinity of the mixture of A and B lectins is due to the A(GalNAcα1->3Gal) sequence. When B4 lectin was tested with Tn, T(Galβ1->3GalNAc), I/II (Galβ1->3/4GlcNAc), and B(Galα1->3Gal) by QPIA, only the Tn determinant was active and it was 14 and 1602 times more active than GalNAc and Gal, respectively. From our current data as well as previous results, it is concluded that the combining site of B4 lectin should be of a cavity type and most specific for Tn. The configuration of carbon-4, an acetylamido group at carbon-2 and α1->Ser/Thr are the major requirements for binding.