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 Cd(7)-BgMTs reconstructed by molecular modeling included two domains: the β-domain with M(3)(S(cys))(9) metal-thiolate clusters and the α-domain with M(4)(S(cys))(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 (T(5)), which may loosen the structure of the β-domain of BgMT-III, and a conserved C(6)PCP(9) motif, which may provide an interacting surface for protein-protein interactions. There is also an acidic hexapeptide insertion (E(55)GAEAE(60)) that could regulate the particular interdomain interactions and lead to the conformational change in the β-domain.