Diversity, structure and regulation of microbial metallothionein: Metal resistance and possible applications in sequestration and detoxification of toxic metals

Metallothioneins (MTs) are group of cysteine rich, universal, low molecular weight proteins distributed widely in almost all major taxonomic groups ranging from tiny microbes to highly organized vertebrates. The primary function of this protein is storage, transportation and binding of metals which enable microorganism to detoxify heavy metals. In microbial world, these peptides were first identified in a cyanobacterium Synechococcus as SmtA protein which exhibit high affinity towards rising level of zinc and cadmium to preserve metal homeostasis in cell. In yeast, MTs aid in reserving copper and confer protection copper toxicity by chelating excess copper ions in cell. Two MTs, Cup1 and Crs5 originated from Saccharomyces cerevisiae predominantly bind to copper though capable of binding with zinc and cadmium ions. MTs superfamily 7 is found in ciliated protozoa which show high affinity towards copper and cadmium. Several tools and techniques such as western blot, capillary electrophoresis, inductively coupled plasma, atomic emission spectroscopy and high performance liquid chromatography have been extensively utilized for the detection and quantification of microbial MTs which is utilized for efficient remediation and sequestration of heavy metals from the contaminated environment.