大珠母贝(Pinctada maxima)金属硫蛋白cDNA克隆与序列特征分析

Cloning and Characterization of a Metallothionein Gene in Silver-lipped Pearl Oyster Pinctada maxima

金属硫蛋白(Metallothionein,MT)是一类普遍存在于生物体内、分子量低、半胱氨酸含量丰富、能够与二价重金属离子结合的蛋白质。MT在清除自由基、解除重金属毒性、参与体内微量元素代谢、防止细胞癌变等方面具有重要作用。本研究通过构建大珠母贝外套膜全长cDNA文库,首次克隆得到大珠母贝金属硫蛋白(PmMT)全长cDNA序列。该序列全长599bp,5’UTR(Untranslated Region)为75bp,3’UTR为296 bp,开放阅读框(Open Reading Frame,ORF)为228bp,编码75个氨基酸。编码的氨基酸中半胱氨酸含量丰富,达到29.3%;赖氨酸和甘氨酸含量也较高,均为9.3%;不含苯丙氨酸、组氨酸、色氨酸、酪氨酸等芳香族氨基酸;含有软体动物等无脊椎动物金属硫蛋白的特征序列。序列特征分析表明,该序列具备金属硫蛋白的典型特征,是金属硫蛋白家族成员。

Metallothioneins （MTs） are a family of proteins with low molecular weight, high cysteine content, and high affinity for divalent heavy metal ions. MT plays an important role in removal of free radicals, detoxification of heavy metal ions, metabolism of trace elements, and preventing the process of oncogenesis. In this study Pinctada maxima MT （PmMT） gene was cloned, sequenced, characterized and expressed in vitro through construction and screening of the full - length cDNA library from the man- de of the oyster. The full - length cDNA of PmMT is 599 bp including a 5＇ untranslated region （UTR） of 75 bp, a 3＇ UTR of 296 hp and an open reading frame （ORF） of 228 bp encoding a polypeptide of 75 amino acids. The contents of Cys, Lys and Gly in the PmMT amino acids sequence were 29. 3%, 9. 3% and 9. 3% , respectively, while no Phe, His, Trp or Tyr were found. Pm- MT presented the typic feature of invertebrat MT, including molluscan. The sequence analysis indicated that PmMT was the member of metallothionein family.