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Characterization of metallothioneins (MT-I and MT-II) in the yak¹

J. P. Wu^*,2, B. Y. Ma^*,,,2, H. W. Ren^,3, L. P. Zhang^*, Y. Xiang and M. A. Brown^||

^* College of Animal Science and Technology, Gansu Agricultural University, Lanzhou, China 730070; and National Key Laboratory of Protein Engineering, Peking University, Beijing, China 100871; and Institute of Biophysics, Chinese Academy of Sciences, Beijing, China 100101; and College of Life Sciences, Beijing Normal University, Beijing, China 100875; and and ^|| Grazinglands Research Laboratory, USDA-ARS, El Reno, OK 73036

³ Corresponding author: renhw{at}pku.edu.cn

The cDNA-encoding sequences for yak metallothionein isoforms I (MT-I) and II (MT-II) were amplified and cloned by reverse-transcription PCR to characterize the nucleotide sequence and protein structure of metallothionein in the yak. The cDNA sequences of MT-I and MT-II were subjected to BLAST searching at the National Center for Biotechnology Information, and the results indicated that the nucleotide sequences of yak MT-I and MT-II, when compared among different species of mammals, are highly conserved. The yak open reading frames have a length of 183 nucleotides, which encode for yak MT-I and MT-II proteins of 61 AA, respectively. Analysis of hydrophobicity, trans-membrane region, and signal peptides suggested that metallothioneins of the yak are nonsecretory proteins. There were several conserved tripeptide sequences, such as C-X-C, C-C-X-C-C, and C-X-X-C (X designates AA excluding cysteine in MT-I and MT-II), and they are highly conserved in their evolution. By homologous comparative modeling, we predicted the molecular spatial structures of yak MT-I and MT-II, which are composed of - and ß-domains that are linked by the conserved tripeptide Lys³⁰-Lys³¹-Ser³² (KKS).

Key Words: cDNA • characterization • metallothioneins • structure • yak

² Both authors contributed equally to this work. Wu Jian-ping: wujp{at}gsau.edu.cn; Ma Bin-yun: maby{at}163.com