Palumaa P, Eriste E, Kruusel K, Kangur L, Jörnvall H, Sillard R
Department of Gene Technology, Tallinn Technical University, Ehitajate tee 5, EE-19086 Tallinn, Estonia.
Cell Mol Biol (Noisy-le-grand). 2003 Jul;49(5):763-8.
Metallothionein-3 (MT-3) is a brain-specific isoform of metallothioneins, which is down-regulated in Alzheimer's disease (AD), inhibits the growth of neurons in vitro, and differs from common MTs also in gene regulation. To elucidate the differences in structure and function between MT-3 and common MTs, Zn2+ and Cd2+ binding to MT-3 and MT-1 were studied using electrospray ionization time of flight mass spectrometry (ESI TOF MS) at pH values between 7.5 and 2.7. The metal binding properties of MT-3 differ considerably from those of MT-1. After reconstitution with a metal excess, metallated MT-3 exists as a mixture of Zn7MT-3 (or Cd7MT-3, respectively) and several metalloforms with stoichiometries below and above seven. In contrast, MT-1 exists as a single Zn7MT-1 (or Cd7MT-1). Lowering of pH leads to a stepwise release of metals from metallated MT-3, first from extra sites, then from the 3-metal cluster and finally from the 4-metal cluster. At acidic pH values the 4-metal cluster of MT-3 is slightly more stable than that of MT-1. The results demonstrate higher structural plasticity, dynamics and metal binding capacity of MT-3 than of MT-1, which makes MT-3 suitable as a zinc buffer-transfer molecule in zinc-enriched neurons functioning at conditions of fluctuating zinc concentrations.
金属硫蛋白-3（MT-3）是金属硫蛋白的一种脑特异性异构体，在阿尔茨海默病（AD）中表达下调，在体外可抑制神经元生长，并且在基因调控方面也与常见的金属硫蛋白不同。为了阐明MT-3与常见金属硫蛋白在结构和功能上的差异，在pH值介于7.5和2.7之间时，使用电喷雾电离飞行时间质谱（ESI TOF MS）研究了锌离子（Zn2+）和镉离子（Cd2+）与MT-3和MT-1的结合情况。MT-3的金属结合特性与MT-1有很大差异。在过量金属重构后，金属化的MT-3以Zn7MT-3（或分别为Cd7MT-3）与几种化学计量比低于和高于7的金属形式的混合物存在。相比之下，MT-1以单一的Zn7MT-1（或Cd7MT-1）形式存在。降低pH值会导致金属从金属化的MT-3中逐步释放，首先从额外的位点释放，然后从三金属簇释放，最后从四金属簇释放。在酸性pH值下，MT-3的四金属簇比MT-1的略稳定。结果表明，MT-3比MT-1具有更高的结构可塑性、动力学和金属结合能力，这使得MT-3适合作为在锌浓度波动条件下起作用的富含锌的神经元中的锌缓冲转移分子。
