Isolation of Metallothionein Genes and in silico Structural Characterization of Their Proteins Using Molecular Modeling from Yak (Bos grunniens)

Yak metallothioneins (BgMTs) are cysteine-rich metal-chelating proteins with highly conserved cysteine residues in their amino acid sequences. The 3D structures of the Cd7-BgMTs reconstructed by molecular modeling included two domains: the β-domain with M3(Scys)9 metal–thiolate clusters and the α-domain with M4(Scys)11 metal–thiolate clusters. An unusual variant was found at position 30 (Cys30→Ser30) in BgMT-III, which is usually conserved in the mammalian MT-I/-II (Cys29) and MT-III (Cys30). The variant residue of BgMT-III may play a key role in yak genetic evolution, metal-binding activity, dynamic conformation, and heavy metal metabolism. BgMT-III contained a Thr insertion at position 5 (T5), which may loosen the structure of the β-domain of BgMT-III, and a conserved C6PCP9 motif, which may provide an interacting surface for protein–protein interactions. There is also an acidic hexapeptide insertion (E55GAEAE60) that could regulate the particular interdomain interactions and lead to the conformational change in the β-domain.