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Part I：Abrin如何經由Translocation而進入細胞質中產生細胞毒性是一
個有趣的問題，本實驗中我們將Abrin A-chain的C端加入KDEL胺基酸序列
，並將此蛋白與Abrin B-chain進行Reassociation．ATA-KDEL蛋白質的N-
glycosidase 活性與reATA是相同的，在Rabbit reticulocyte lysates
cell free protein synthesis的研究方面發現，兩者對蛋白質合成的抑
制作用也是相同的．然而，在對細胞蛋白質合成抑制作用的研究方面則發
現將Abrin A-chain的C端加入KDEL序列後能使Abrin A鏈對Vero細胞的細
胞毒性增加14倍，另外亦能使Abrin對Vero細胞的細胞毒性增加4.5倍．因
此本實驗建議修飾過的Abrin A-chain及Abrin能經由ER進行
Translocation而進入細胞質中，也因此增加其細胞毒性．Part II：
Abrin A-chain具有N-glycosidase活性，另外也可能具有Apoptosis的功
能，有證據顯示核醣體蛋白質與A鏈的交互作用對其N-glycosidase活性有
很大的影響．究竟細胞內有哪些蛋白質能與Abrin A-chain能直接交互作
用呢？本實驗利用GST-pull down assay及reATA-Sepharose 4B親和性管
柱發現Rat liver lysates中有4種主要的蛋白質可能與Abrin A鏈直接交
互作用，分子量以SDS-PAGE分析分別為70,000，65,000，43,000及34,000
．
Part I: Abrin consists of a 35-kDa lectin B-chain disufide
linked to a 28-kDarRNA N-glycosidase A-chain. Abrin B-chain
binds mammalian cell surface glycoproteins and triggers
internalization and routing of the toxin to anintracellular
vesicle, from which abrin A-chain released and translocates to
the cytosol. In the cytosol, abrin A-chain catalytically
inactivates protein synthesis. Although the translocation-
competent intracelular vesicle for abrinis unknown, several
pieces of evidence point to the ER. In this work we have shown
that the addition of an ER retention signal to the C-terminus of
the A-chain can significantly enhance the cytotoxicity of the
already extremely potent toxin abrin by 4.5 fold. We suggested
that ATB-ATAKDEL may swich receptor in the trans-reticular Golgi
and bind galactosylated ER luminal proteins, which are returned
to the ER by carrying a KDEL motif. Part II: The ribosomal
proteins play an important role in making rRNA highlysusceptible
to attack by Abrin A-chain was established by Endo, who showned
that rat rRNA in the context of the ribosome is depurinated at
adenine 4324by abrin A-chain with a Kcat nearly 100,000-fold
greater than that measured using naked 28S rRNA. Exactly which
ribosomal proteins are involved and the nature of their
contribution to the increased efficiency of catalysis by
ribosome-inactivating proteins remains to be determined. In this
work we haveshown that abrin A-chain may directly interact with
four proteins derived from rat liver lysates. They have
molecular size of 70-kDa, 65-kDa, 43-kDa and 34-kDa analyzed by
SDS-PAGE. The further characterization of four proteins is
needed to be done.
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