Cloning of oligopeptide transport carrier PepT1 and comparative analysis of PepT1 messenger ribonucleic acid expression in response to dietary nitrogen levels in yak (Bos grunniens) and indigenous cattle (Bos taurus) on the Qinghai–Tibetan plateau1

The gastrointestinal lumen can directly absorb all diand tripeptide protein degradation products, and oligopeptide absorption depends on the specific peptide transport carriers, which are located in gastrointestinal epithelial cells on the brush border membrane. Yak (Bos grunniens) use N more efficiently than cattle do, which implies that yak have a specific mechanism of nonprotein utilization including a peptide absorption mechanism. However, this mechanism has not been clarified. Our objective was to explore whether yak possess any adaptive mechanisms of peptide absorption to survive in the harsh foraging environment of the Qinghai–Tibetan plateau. Twelve castrated males of each of 2 genotypes, yak (B. grunniens) and indigenous cattle (Bos taurus), were fed diets of various N levels. The yak PepT1 (yPepT1) cDNA was cloned in omasum epithelial tissue. Our results showed that the full-length yPepT1 cDNA contains 2,805 bp, and a 2,121-bp open reading frame encodes a putative protein of 707 AA residues. The yPepT1 AA sequence identified 5 putative extracellular N-glycosylation sites (Asn406, Asn434, Asn438, Asn498, and Asn508), 2 putative intracellular protein kinase A sites (Ser271 and Thr359), and 3 intracellular putative protein kinase C sites (Ser252, Ser266, and Ser357). The yPepT1 AA sequence was 99, 95, 86, and 83% identical to PepT1 from cattle (B. taurus), sheep (Ovis aries), pigs (Sus scrofa), and humans (Homo sapiens), respectively. The relative PepT1 mRNA expression for indigenous cattle was greater than yak in the rumen, omasum, duodenum, ileum, and liver (P < 0.001); however, it was lower in jejunum tissue (P < 0.01). The relative PepT1 mRNA expression in response to increasing dietary N for both genotypes were linear in the rumen and jejunum (P < 0.10); quadratic or cubic in the reticulum (P < 0.01); linear or quadratic in the duodenum, ileum, and liver (P ≤ 0.01); and linear, quadratic, or cubic in the omasum (P < 0.001). Moreover, there were significant interactions between genotype and dietary N in rumen, reticulum, omasum, duodenum, jejunum, ileum, and liver tissues. In conclusion, the PepT1 profile and expression in gastrointestinal epithelial cells of yak varied from those of cattle, implying that yak have evolved a peptide transport mechanism to adapt the environment of the Qinghai–Tibetan plateau.