The expressed alpha domain of mouse metallothionein-I from Escherichia coli displays independent structure and function.

The alpha domain of mouse metallothionein-I (mMT-I) was expressed in E. coli as a C-terminus of the 26 KD glutathione-S-transferase and purified from the cell lysates. The amino acid composition and molecular weight of the expressed protein are as expected. The metal-binding stoichimetry was determined to show that divalent metals bind to the expressed alpha domain at the desired ratio of 4:1. The ultraviolet absorbance, circular dichroism spectra and the atomic force microscopy indicate that it can form the proper metal-thiolate structure as in the whole MT molecule. The apparent affinity of the expressed alpha domain to bind cadmium is 1.8-fold stronger than the recombinant mMT-I when detected by the reaction with DTNB. The ability to scavenge hydroxyl free radicals remains higher than the whole MT molecule. All the results demonstrate that the expressed alpha-domain from E. coli exhibits independent biochemical and physiological structure/function without the assistance of beta domain.