Chow L P, Chou M H, Ho C Y, Chuang C C, Pan F M, Wu S H, Lin J Y
Institute of Biochemistry, College of Medicine, National Taiwan University, Taipei, Republic of China.
Biochem J. 1999 Feb 15;338 ( Pt 1)(Pt 1):211-9.
The seeds of the plant Trichosanthes anguina contain a type I ribosome-inactivating protein (RIP), designated trichoanguin, which was purified to apparent homogeneity by the combined use of ion-exchange chromatographies, i.e. first with DE-52 cellulose and then with CM-52 cellulose. The protein was found to be a glycoprotein with a molecular mass of 35 kDa and a pI of 9.1. It strongly inhibits the protein synthesis of rabbit reticulocyte lysate, with an IC50 of 0.08 nM, but only weakly that of HeLa cells, with an IC50 of 6 microM. Trichoanguin cleaves at the A4324 site of rat 28 S rRNA by its N-glycosidase activity. The cDNA of trichoanguin consists of 1039 nt and encodes an open reading frame coding for a polypeptide of 294 amino acid residues. The first 19 residues of this polypeptide encode a signal peptide sequence and the last 30 residues comprise an extension at its C-terminus. There are four potential glycosylation sites, located at Asn-51, Asn-65, Asn-201 and Asn-226. A comparison of the amino acid sequence of trichoanguin with those of RIPs such as trichosanthin, alpha-momorcharin, ricin A-chain and abrin A-chain reveals 55%, 48%, 36% and 34% identity respectively. Molecular homology modelling of trichoanguin indicates that its tertiary structure closely resembles those of trichosanthin and alpha-momorcharin. The large structural similarities might account for their common biological effects such as an abortifacient, an anti-tumour agent and anti-HIV-1 activities. Trichoanguin contains two cysteine residues, Cys-32 and Cys-155, with the former being likely to be located on the protein surface, which is directly amenable for conjugation with antibodies to form immunoconjugates. It is therefore conceivable that trichoanguin might be a better type I RIP than any other so far examined for the preparation of immunotoxins, with a great potential for application as an effective chemotherapeutic agent for the treatment of cancer.
绞股蓝种子含有一种I型核糖体失活蛋白（RIP），称为绞股蓝蛋白，通过离子交换色谱法联用，即先用DE - 52纤维素，再用CM - 52纤维素，将其纯化至表观均一性。该蛋白被发现是一种糖蛋白，分子量为35 kDa，pI为9.1。它强烈抑制兔网织红细胞裂解物的蛋白质合成，IC50为0.08 nM，但对HeLa细胞的抑制作用较弱，IC50为6 μM。绞股蓝蛋白通过其N - 糖苷酶活性在大鼠28 S rRNA的A4324位点切割。绞股蓝蛋白的cDNA由1039个核苷酸组成，编码一个开放阅读框，编码一个294个氨基酸残基的多肽。该多肽的前19个残基编码一个信号肽序列，最后30个残基构成其C末端的延伸。有四个潜在的糖基化位点，位于Asn - 51、Asn - 65、Asn - 201和Asn - 226。将绞股蓝蛋白的氨基酸序列与天花粉蛋白、α - 苦瓜素、蓖麻毒素A链和相思子毒素A链等RIPs的氨基酸序列进行比较，分别显示出55%、48%、36%和34%的同一性。绞股蓝蛋白的分子同源性建模表明，其三级结构与天花粉蛋白和α - 苦瓜素的三级结构非常相似。较大的结构相似性可能解释了它们共同的生物学效应，如堕胎、抗肿瘤和抗HIV - 1活性。绞股蓝蛋白含有两个半胱氨酸残基，Cys - 32和Cys - 155，前者可能位于蛋白质表面，可直接用于与抗体偶联形成免疫偶联物。因此可以想象，绞股蓝蛋白可能是一种比迄今为止研究的任何其他I型RIP更好的用于制备免疫毒素的蛋白，具有作为治疗癌症的有效化疗药物的巨大应用潜力。
