title: The effects of the carboxyl-terminus amino acids of the Shiga toxin             B-subunit on retrograde transport.
abstract: The Shiga toxin B-subunit (STxB), from the enteric pathogen, Shigella dysenteriae, is responsible for the attachment of its receptor, globotriaosylceramide (Gb3), and navigates the retrograde pathway from the plasma membrane to the endoplasmic reticulum (ER). In this study, in order to demonstrate the role of carboxyl-terminus (C-terminus/al) amino acids of the B-fragment on the retrograde transport speed and the retrograde transport pathway, STxB was modified by site-directed mutagenesis and by the addition of an amino acid tail. The results showed that when the C-terminal amino acid, arginine [Arg (R)], was mutated to serine [Ser (S)], the speed of the B-fragment transportation into the ER at 37 ˚C was slower. When an acidic amino acid tail 'glutamine (Glu)-Ser' (ES) was added to the C-terminal amino acid 'R', the B-fragment transporting speed slowed down and remained in the Golgi apparatus. Further experiments showed that the effects induced by mutations of the amino acid tail resulted in STxB-EEEES ≥-EEES>-EES>-ES, demonstrating that the retardation effect on the tail was increased and the length of the acidic amino acid was augmented. The effect was possibly produced by an acidic amino acid tail, not only by the amino acid 'E'. The significant inhibitory effect on the speed of B-fragment retrograde transport was observed only when the mutations of the acidic amino acid tail were linked near to the C-terminus. These results may provide important insights for the study of transport mechanisms and for the development of STxB serial proteins as vectors for drug delivery.
authors.affiliation: School of Life Sciences, Northeast Normal University, Changchun, Jilin 130024, PR China.
authors.forename: Dan
authors.initials: D
authors.lastname: Liu
authors.forename: Yuying
authors.initials: Y
authors.lastname: Fan
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: Xiaoge
authors.initials: X
authors.lastname: Gao
authors.forename: Miao
authors.initials: M
authors.lastname: Hao
authors.forename: Huiting
authors.initials: H
authors.lastname: Xue
authors.forename: Guihua
authors.initials: G
authors.lastname: Tai
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D024342:Amino Acids, Acidic / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D022603:Shiga Toxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D024342:Amino Acids, Acidic; D022603:Shiga Toxins; C077239:stxB toxin