CYANOBACTERIAL METALLOTHIONEIN GENE EXPRESSED IN ESCHERICHIA-COLI - METAL-BINDING PROPERTIES OF THE EXPRESSED PROTEIN

The recently isolated Synechococcus gene smtA encodes the only characterised prokaryotic protein designated to be a metallothionein (MT). To examine the metal-binding properties of its product the smtA gene was expressed in Escherichica coli as a carboxyterminal extension of glutathione-S-transferase. The pH of half dissociation of Zn, Cd and Cu ions from the expressed protein was determined to be 4.10, 3.50, 2.35. respectively, indicating a high affinity for these ions (in particular for Zn in comparison to mammalian MT). E coli expressing this gene showed enhanced (ca. 3-fold) accumulation of Zn.