Polymorphisms, Molecular Characteristics of LGB Gene in River and Swamp Buffalo (Bubalus bubalis)

Beta-lactoglobulin (β-LG) is the major whey protein associated with lactation traits in ruminants and has a potential impact on human health. So far, the polymorphisms and molecular characteristics of buffalo LGB gene have not been well understood. In this study, the complete coding sequence (CDS) of buffalo LGB were isolated and its polymorphisms were detected using direct sequencing of PCR product. The CDS of LGB gene for river and swamp buffalo was 543 nucleotides in length, encoding a peptide with 180 amino acid residues. A total of eight single nucleotide polymorphisms (SNPs) was identified in the CDS of LGB gene in two types of buffalo. Among them, c.46G>A and c.131C>T were non-synonymous, which led to an amino acid substitution from Ala to Thr at the 16th position of the signal peptide and a p.Ala26Val substitution in the mature peptide of buffalo β-LG, respectively. The prediction showed that the p.Ala26Val may affect the function of buffalo β-LG. Seven LGB haplotypes were defined based on the SNPs observed in buffalo, and accordingly, two variants and two synonymous variants of buffalo β-LG were inferred, named variant A, A 1 , A 2 and B, respectively. All the variants determined in buffalo did not exist in the animals of Bos genus. The sequence alignment of β-LG mature peptide showed that there were two different amino acids (p.Ile1Leu and p.Val162Ile) between buffalo and the animals of Bos genus. The signal peptide of buffalo β-LG was two amino acids longer than that of Bos genus and there was an differential amino acid at the 13th position of signal peptide, which may lead to different functions of signal peptide between buffalo and Bos genus. The hydrophilicity of buffalo β-LG variants A and B were slightly different, and their physicochemical characteristics were similar to those of cattle β-LG B. The mature peptides of β-LG in buffalo and Bos genus had a lipocalin domain, which revealed that they had the same function. This study will give us new insights into the variation, physicochemical characteristics and biological function of buffalo LGB gene.