Del Vecchio Blanco F, Bolognesi A, Malorni A, Sande M J, Savino G, Parente A
Dipartimento di Chimica Organica e Biologica, Università di Napoli Federico II, Italy.
Biochim Biophys Acta. 1997 Mar 7;1338(1):137-44. doi: 10.1016/s0167-4838(96)00182-3.
The primary structure has been determined for PD-S2, a new type 1 ribosome-inactivating protein (RIP), isolated from the seeds of Phytolacca dioica L. PD-S2 has 265 amino-acid residues, and a molecular mass of 29586 Da. The polypeptide chain contains four amino-acid residues more than PAP-S, a type-I RIP isolated from the seeds of the taxonomically related plant Phytolacca americana L. We have compared the amino-acid sequence of PD-S2 with those of two other RIPs with known three-dimensional structure: PAP-S and ricin A-chain (RTA), the active chain of the best known type-2 RIP. This analysis shows an identity of 76% and 33% with PAP-S and RTA respectively, and a similarity of 82% and 54%. Comparison with the PAP sequence, isolated from leaves of P. americana, shows an even higher identity (80%) and similarity (87%). Furthermore, the amino-acid residues reported in other RIPs to be invariant and participate in the definition of the active site (Tyr-76, Tyr-127, Glu-179, Arg-182 and Trp-211; PD-S2 numbering) are all present. Asn-74, Arg-138, Gln-175, and Glu-208 are also conserved, while Asn-209 is substituted by Glu, all residues located in the active-site cleft of RIPs (Tahirov, T.H., Lu, T.-H., Liaw, Y.-C., Chen, J.L. and Lin, J.Y. (1995) Crystal structure of abrin-a at 2.14 A, J. Mol. Biol. 250, 354-367). The polypeptide chain of PD-S2 contains two N-glycosylation sites at Asn-112 and Asn-120, the second of which appears to be linked to sugars. Like PAP-S, PD-S2 does not contain free sulfhydryl groups. The four cysteinyl residues of the two proteins have corresponding sequence positions, most likely with identical S-S pairing.
已确定从商陆（Phytolacca dioica L.）种子中分离出的新型1型核糖体失活蛋白（RIP）PD-S2的一级结构。PD-S2含有265个氨基酸残基，分子量为29586道尔顿。该多肽链比从分类学上相关的植物美国商陆（Phytolacca americana L.）种子中分离出的I型RIP PAP-S多四个氨基酸残基。我们已将PD-S2的氨基酸序列与另外两种具有已知三维结构的RIPs的氨基酸序列进行了比较：PAP-S和蓖麻毒素A链（RTA），后者是最著名的2型RIP的活性链。该分析表明，PD-S2与PAP-S和RTA的同一性分别为76%和33%，相似性分别为82%和54%。与从美国商陆叶片中分离出的PAP序列相比，同一性（80%）和相似性（87%）更高。此外，在其他RIPs中报道的不变且参与活性位点定义的氨基酸残基（Tyr-76、Tyr-127、Glu-179、Arg-182和Trp-211；PD-S2编号）均存在。Asn-74、Arg-138、Gln-175和Glu-208也保守，而Asn-209被Glu取代，所有这些残基都位于RIPs的活性位点裂隙中（Tahirov，T.H.，Lu，T.-H.，Liaw，Y.-C.，Chen，J.L.和Lin，J.Y.（1995年）相思子毒素-a在2.14埃处的晶体结构，《分子生物学杂志》250，354-367）。PD-S2的多肽链在Asn-112和Asn-120处含有两个N-糖基化位点，其中第二个似乎与糖相连。与PAP-S一样，PD-S2不含游离巯基。这两种蛋白质的四个半胱氨酸残基具有相应的序列位置，最有可能具有相同的S-S配对。
