Alternate immunoactivation pathway for a plant lectin from Rosar

Alternate immunoactivation pathway for a plant lectin from Rosary pea


(Abrus precatorious)


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- Date/Time : Tue., 16 July 2002


   15:00-16:00 

- Speaker :Dr. T.K. Maiti (Assistant prof.)


               - Dept. of Biotechnology


               - IIT Kharagpur, INDIA


 

- Place : Life Science Bldg. #104

- For inquires : Professor Hong Gil Nam Dept. of Life Science


                  생명과학과 남홍길 교수 (☎279-2111)

- Abstract


Abrus precatorius or Indian licorice is the source of two plant lectins abrin, apotent toxin and the agglutinin, which is the dimeric association of two toxin sub unit but it is less toxic.  The toxin abrin is approve ribosome inhibiting protein and its  mode of action has been elucidatted  long since. A key step in the endocytosis of the toxin is the recogniyion of the saccharide -binding pocket in the chain B by cell surface saccharide receptors, which is prelude to activation. The agglutinin  can proliferate murine splenocytes at ng/ml concentration but inhibits at higher concentration at microgram/ml ranges. We had observed that on heat denaturing the protein, the lactose binding  activity was lost, which was verified  by RBC agglutination experiments. Yet , the protein shoed increased splenocyte proliferation and on trypsinization of the protein, the activity increased dramatically. It has also been observed that the hear denatured agglutinin canmact as a potent adjuvant. Individually, neither  chain A nor chain B could stimulate proliferation in any form ( native/heat denatured/ trypsinized). These results led us to surmise that there must exist an alternate activation pathway that does not involve the saccharide  receptor. We suspected the existence of certain immunostimulatory regions in the protein, and theoritical analysis we carried out in this direction. A custom sequence similarity alogrithm was devised to search for known immunostimulatory peptide sequences in the entirelength of agglutinin. It was found that these peptide sequences would be conserved even after complete trypsin digestion.Moreover, two of these imunostimulatory sequences were found to be strategically located both with respect to themselves and with respect to the disulfide bond linking the A and B chains of the heterodimer.