志贺毒素B亚基C-末端氨基酸序列对其胞内逆向运输的影响

he B subunit of Shiga toxin (STxB) from enteric pathogens Shigella dysenteriae, is responsible for the attachment of its receptor globotriaosyl ceramide (Gb3), navigate the retrograde pathway from the plasma membrane to the endoplasmic reticulum. In order to demonstrate the role of end amino acid at carboxyl-terminus (C-terminus) of B-fragment on its retrograde transport speed and pathway, Shiga toxin B-subunit was modified by site-directed mutagenesis and addition of amino acid tail. The results showed that, when the end amino acid Arg (R) was mutated to be Ser (S), the speed of B-fragment transported into endoplasmic reticulum (ER) at 37 ℃ was slower. When adding acidic amino acid tail "Glu-Ser" (ES) behind the end amino acid "R", B-fragment transporting speed slowed down and tended to remain in Golgi apparatus. Further studies showed that the effects induced by the mutations of amino acid tail were STxB-EEEES≥-EEES>-EES>-ES, suggesting that the retarded effect of the tail was increased along with the length of acidic amino acid augmented. The effect was probably produced by acidic amino acid tail, not only by amino acid "E". The significant inhibitory effect on the speed of B-fragment retrograde transport was observed only when the mutations of acidic amino acid tail were linked near to C-terminus. These results might be important to study transport mechanism and develop Shiga toxin B serial proteins as drug vectors.