Computational Molecular Analyses of Kappa Casein 3 Gene in 24 Species Reveal Differences Between Ruminants and Non-Ruminant Mammals

Kappa casein 3 (CSN3) is a variant member of caseins, a family of phosphoproteins that account for nearly 80% of bovine milk proteins and highly conserved in mammalian species. Fifty-eight CSN3 gene sequences with corresponding amino acids in 24 mammalian species (cattle, goat, sheep, buffalo, yak, giraffe, deer, chamois, gaur, goral, gazelle, grysbok, camel and blue duiker classified as ruminant mammals based on stomach complexity and ten divergent taxa of human, pig, monkey, zebra, horse, mouse, ass, rat, guinea pig and rabbit) were analysed using a comparative genomics approach. The aligned sequences showed high level of polymorphism in CSN3 sequences among the species. Results revealed high level of identity and similarity among the ruminants (81-99% and 82-100%) except for camel indicating high conservation among ruminants. Values of identity and similarity of CSN3 in ruminants compared to non-ruminant mammalian species suggest that the CSN3 protein may be functionally different in non-ruminants and may point to a more ancient divergence between them. Amino acids exhibited higher polymorphisms among species than within species. Our analysis revealed 4 non-synonymous polymorphisms in cattle, 6 in goats, 4 in horses, 3 in rabbits and 7 in sheep. Haplotype diversity was 1.00 in the mouse, rabbit, goat, horse, camel, sheep and human indicating abundant genetic diversity in these species. The close relationship among members of the Bos and Equus genera from the constructed phylogenetic trees of CSN3 gene suggest evolutionary proximity characteristic of a more recent common ancestor.