Orrù S, Scaloni A, Giannattasio M, Urech K, Pucci P, Schaller G
Centro Internazionale di Servizi di Spettrometria di Massa del CNR, Napoli, Italy.
Biol Chem. 1997 Sep;378(9):989-96. doi: 10.1515/bchm.1997.378.9.989.
The complete primary structure of a cytotoxic 5 kDa polypeptide, viscotoxin A1, isolated from Viscum album L., has been determined by combining classical Edman degradation methodology with advanced mass spectrometric procedures. The same integrated approach allowed correction of the sequence of viscotoxin A2 and definition of the pattern of the disulfide bridges. The arrangement of the cysteine pairing was determined as Cys3-Cys40, Cys4-Cys32 and Cys16-Cys26. The primary structure of viscotoxin A1 shares a high degree of similarity with the known viscotoxins and more generally with the plant alpha- and beta-thionins. The pattern of S-S bridges determined for viscotoxin A2 and A1 is similar to that inferred by X-ray and NMR analysis in crambin and related to that present in alpha-purothionin and beta-hordothionin, thus indicating a highly conserved organization of the S-S pairings within the entire family. This arrangement of S-S bridges describes a peculiar structural motif, indicated as 'concentric motif', which is suggested to stabilize a common structure occurring in various small proteins able to interact with cell membranes. The distribution of the new variant toxin in different mistletoe subspecies was investigated. Viscotoxin A1 is abundant in the seeds of the three European subspecies of V. album whereas it represents a minor component in the shoots.
通过将经典的埃德曼降解方法与先进的质谱程序相结合，已确定了从欧洲槲寄生中分离出的一种细胞毒性5 kDa多肽——槲寄生毒素A1的完整一级结构。同样的综合方法使得能够校正槲寄生毒素A2的序列并确定二硫键模式。半胱氨酸配对的排列确定为Cys3-Cys40、Cys4-Cys32和Cys16-Cys26。槲寄生毒素A1的一级结构与已知的槲寄生毒素高度相似，更普遍地与植物α-和β-硫堇相似。为槲寄生毒素A2和A1确定的S-S桥模式与通过X射线和核磁共振分析在胰凝乳蛋白酶原中推断的模式相似，并且与α-小麦硫蛋白和β-大麦硫堇中的模式相关，因此表明整个家族中S-S配对的组织高度保守。这种S-S桥的排列描述了一种特殊的结构基序，称为“同心基序”，它被认为可以稳定各种能够与细胞膜相互作用的小蛋白质中出现的共同结构。研究了新变体毒素在不同槲寄生亚种中的分布。槲寄生毒素A1在欧洲槲寄生的三个亚种的种子中含量丰富，而在嫩枝中它是次要成分。
