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Kamal Usman, Bashir Sajo Mienda, Shehu Idris, Zainab Ladidi Idris

Metallothioneins are usually low molecular weight metal binding proteins which were first discovered in the late 1950s following an intensive study of yeast, mammals and plants. Among the four subfamilies or classes of plant metallothioneins, Type 4 plant metallothioneins (PMTs), metallothioneins 4 (MT4) or early cysteine as popularly known, stands out to be the most intensively studied group in vitro, perhaps this is attributed to their peculiar structure and function coupled with ease of isolation and purification when compared to other metallothioneins (MTs). In a recent study on barley (Hordeum vulgare) a member of this group revealed that MT4 genes of the plant show local zinc binding in the grain aleuronic layer and act in putative storage. However, structural information and understanding of metal binding dynamics of these MTs are scanty, with early cysteine metallothioneins (MT) from wheat as the only PMT with crystal 3D structure currently available. This paper reviews the state of researches on the structure and functions of Type 4 plant metallothioneins and considering their proposed function which includes provision of Zn (II) to the relevant processes during seed germination, it will be interesting to find out about its ability to transfer Zn (II) ions to other molecules.