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Title: CHARACTERIZATION OF METALLOTHIONEINS (MT-I AND MT-II) IN YAK

Author
item WU, JIANPING - GANSU AG. UNIV.
item MA, BINYUN - GANSU AG. UNIV.
item REN, HONGWEI - GANSU AG. UNIV.
item ZHANG, LIPING - GANSU AG. UNIV.
item XIANG, YUN - GANSU AG. UNIV.
item Brown, Michael

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2006
Publication Date: 2/28/2007
Citation: Wu, J., Ma, B., Ren, H., Zhang, L., Xiang, Y., Brown, M.A. 2007. Characterization of metallothioneins (mt-i and mt-ii) in yak. Journal of Animal Science. 85:1357-1362.

Interpretive Summary: Heavy metals, hormones, inflammation, acute stress, and many chemicals can induce activity in two isoforms of the metallothionein multigene family (MT-I and MT-II). Metallothioneins act as free radical scavengers, and protect against toxicity of alkylating anticancer drugs and other electrophiles. Yak (Bos grunniens) represents a unique bovine species adapted to the Qinghai-Tibetan plateau of China at altitudes of 3,000 meters above sea level. Yak are usually the dominant species in such environments that are ill-suited for cattle or sheep and yak are used for meat, milk, draft and fiber. They are a major economic resource to herders in this region. There is a need to evaluate the isoforms of metallothioneins in this species to aid in determination of potential tolerance to the heavy metal contaminants. Research from Gansu Agricultural University (GSAU) determined that the MT-I coding sequences of sheep, cow, pig, and human shared 96%, 95%, 93%, and 89% homology with yak, respectively; the MT-II coding sequences of cow, human, mouse and pig shared 97%, 92%, 92%, and 91% homology with yak, respectively. Analysis of characterization and structure indicated that metallothioneins of yak are highly conservative, low-molecular weight (approximately 6,000 daltons), Cys-rich metal-binding non-secretory proteins, in which there is no obvious hydrophobicity, transmembrane regions or signal peptides. Thus, tolerances to heavy metal contamination are expected to parallel those of other species. However there is a need for further study of MT-III and MT-IV which may be helpful to fully understand the characteristics of metallothionein activity in yak.

Technical Abstract: In order to characterize nucleotide sequence and protein structure of metallothionein in yak, the yak MT-I and MT-II cDNA encoding sequences were amplified and cloned by RT-PCR. The cDNA sequences of MT-I and MT-II were subjected to BLAST searching at NCBI and the results indicate that the nucleotide sequences of yak MT-I and MT-II, when compared among different species of mammals are highly conservative. The yak Open Reading Frames have a length of 183 nucleotides which encode for yak MT- and -II proteins of 61 amino acids, respectively. Analysis of hydrophobicity, transmembrane region and signal peptides suggest that MTs of yak are non-secretory proteins. There are several conserved tripeptide sequences, such as C-X-C, C-C-X-C-C and C-X-X-C, and they are highly conservative in their evolution. By homologous comparative modeling, we have predicted the molecular spatial structures of yak MT-I/-II, which are composed of alpha and beta domains that are linked by a conserved tripeptide KKS. The MT-I coding sequences of sheep, cow, pig, human shared 96%, 95%, 93%, and 89% homology with yak, respectively; the MT-II coding sequences of cow, human, mouse and pig shared 97%, 92%, 92%, and 91% homology with yak, respectively. Analysis of characterization and structure indicated metallothioneins of yak are highly conservative, low-molecular weight (approximately 6,000 daltons), Cys-rich metal-binding non-secretory proteins, in which there are no obvious hydrophobicity, transmembrane regions signal peptides. Thus, tolerances to heavy metal contamination are expected to parallel those of other species.