Introduction Metallothioneins (MTs) Metallothionein (MT) proteins are characterized as low molecular weight, cysteine-rich, metal-binding proteins [1] . The first MT was discovered more than 50 years ago as Cd 2+ -binding proteins present in horse kidney. Since then, the genes encoding MT proteins have been identified in the animal and plant kingdom as well as in prokaryotes like Synechococcus sp. Due to such diversity in occurrence, their function is still a debatable issue, yet it is unequivocally proven that the MTs are involved in homeostasis and transport of physiologically essential metals ions viz. Zn 2+ and Cu 1+ and detoxification/sequestration of toxic metal ions like Cd 2+ , Hg 2+ etc. Besides, their role in protection against oxidative stress, regulation of cell proliferation and apoptosis, and maintenance of cellular redox balance is also well evident [2-5] . In a recent search using ScienceDirect, it was found that the number of publications under key word “Metallothionein” each year has increased from 1962 to late 2009, totaling 3494 scientific papers in this subject. Looking at the trend (Figure 1), it is clear that the interest in metallothionein has remarkably increased after eighties, and more recently between 2006 and 2009, the publication average recorded more than three papers per week. Further, it is quite clear from the figure that the interest in plant and bacterial MTs has been rather modest as compared to the overall metallothionein research field. But the trend showing an increased researched activity was clearly discernable in the figure. Understandably, the major share of the publication has come out of the work in animals and human. One of the likely reasons towards animal bias was that MTs were associated with diseases related to metal toxicity in human. Another reason for relatively less number of publications was more to do with technical reason of the difficulties in isolation of MTs from plants and bacteria. Besides this, as reported in earlier studies [9] the proteins were hard to be cleaved from the recombinantly expressed proteins in E. coli by proteolytic digestion. With an advent of time these problems were sorted out by way of application of fusion proteins for protein overexpression, and concomitantly more information on the basic properties of plant and bacterial MTs started to gather. The three dimensional structural data of MTs was also exclusively available from animal sources, and the recent development of structural characterization using techniques of NMR, crystallography and mass spectrometry has given adequate insight in the structure of plant and bacterial MTs. Figure 1. Number of publications from 1964 to 2009 searched using keywords “Metallothionein” (green line), “Bacterial Metallothionein” (red line) and “Plant Metallothionein” (black line). Web. Animal MTs have implications in inherited and occupational diseases that are linked to metabolic disorders in the handling of metal ions. Interestingly, MTs also have relevance in diagnosis of certain metal toxicosis disorders from the fact that they can serve as biomarkers, and in some cases even in cure (X-reference). The classical examples of the diseases are Menkes and Wilson’s disease (Table 1