Tomas M, Pagani M A, Andreo C S, Capdevila M, Atrian S, Bofill R
Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain; Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain.
Centro de Estudios Fotosintéticos y Bioquímicos, CONICET, Suipacha 531, 2000 Rosario, Argentina.
J Inorg Biochem. 2015 Jul;148:35-48. doi: 10.1016/j.jinorgbio.2015.02.016. Epub 2015 Feb 28.
Plant metallothioneins (MTs) constitute a family of small Cys-rich proteins capable of coordinating metal ions, significantly differing from microbial and animal MTs. They are divided into four subfamilies depending on the Cys pattern in their sequence. In this work, the MT system of the sunflower plant (Helianthus annuus) has been defined, with ten genes coding for MTs (HaMT) belonging to the four plant MT subfamilies; three HaMT1, four HaMT2, one HaMT3 and two HaMT4 isoforms. The gene expression pattern and capacity to confer metal resistance to yeast cells have been analysed for at least one member of each subfamily. The divalent metal ion-binding abilities of HaMT1-2 and HaMT2-1 (the isoforms encoded by the most abundantly expressed HaMT1 and HaMT2 isogenes) have been characterised, as HaMT3 and HaMT4 were previously studied. Those isoforms constitute an optimum material to study the effect of Cys number variability on their coordination abilities, as they exhibit additional Cys residues regarding the canonical Cys pattern of each subfamily. Our results show that the variation in the number of Cys does not drastically modify their M(II)-binding abilities, but instead modulates the degree of heterogeneity of the corresponding recombinant syntheses. Significantly, the Zn(II)-HaMT1 complexes were highly susceptible to proteolytic cleavage. The recombinant Cd-MT preparations of both isoforms exhibit significant acid-labile sulphide content-Cd6S8 or Cd7S7 species. Overall results suggest that HaMT2-1 is probably associated with Cd(II) detoxification, in contrast to HaMT1-2, which may be more related to physiological functions, such as metal ion transport and delivery.
植物金属硫蛋白（MTs）构成了一类富含半胱氨酸的小蛋白家族，能够与金属离子配位，与微生物和动物的MTs有显著差异。根据其序列中的半胱氨酸模式，它们被分为四个亚家族。在这项工作中，已确定了向日葵植物（Helianthus annuus）的MT系统，有10个编码MTs（HaMT）的基因，属于四个植物MT亚家族；分别为3个HaMT1、4个HaMT2、1个HaMT3和2个HaMT4亚型。已对每个亚家族的至少一个成员的基因表达模式以及赋予酵母细胞金属抗性的能力进行了分析。HaMTl-2和HaMT2-1（由表达最丰富的HaMT1和HaMT2同基因编码的亚型）的二价金属离子结合能力已得到表征，因为之前已对HaMT3和HaMT4进行过研究。这些亚型构成了研究半胱氨酸数量变异性对其配位能力影响的最佳材料，因为它们相对于每个亚家族的典型半胱氨酸模式都有额外的半胱氨酸残基。我们的结果表明，半胱氨酸数量的变化不会大幅改变它们与M（II）的结合能力，而是调节相应重组合成的异质性程度。值得注意的是，Zn（II）-HaMT1复合物极易被蛋白酶切割。两种亚型的重组镉-MT制剂都表现出显著的酸不稳定硫化物含量——Cd6S8或Cd7S7物种。总体结果表明，与可能更多地与金属离子运输和传递等生理功能相关的HaMT1-2相反，HaMT2-1可能与镉（II）解毒有关。
