cDNA sequence analysis, recombinant expression of the inhibin α-subunit of the yak (Bos grunniens)

Inhibin plays an important role in the regulation of reproduction in mammalian species. The objectives of this study were to analyse cDNA sequence and produce recombinant yak inhibin -subunit protein in Escherichia coli by optimising the expression conditions. By reverse transcriptase-polymerase chain reaction (RT-PCR) strategy, we obtained full-length yak inhibin -subunit cDNA sequence comprised of an open reading frame of 1080 bp encoding a 360-amino acid protein with a predicted molecular mass of 38.8 kDa. The predicted protein sequence includes 4 possible proteolytic cleavage sites, 12 evolutionarily conserved cysteine residues and 2 potential N-linked glycosylation sites. The mature subunit is the carboxyl terminal fragment (C-fragment) consisting of 134 amino acids. The full-length precursor protein shared 79.6-98.6% protein sequence identity with mammalian homologues. It exhibited the highest identity with that of cattle (98.6%); there were five amino acid substitutions between these two species. The homology is not evenly distributed with the highest level for the putative C-fragment (77.1-99.3%). The recombinant yak inhibin -subunit protein was successfully expressed in E. coli for the first time.