Sequence, Phylogenetic and Homology Analysis of Toll-Like Receptor Gene TLR7 in Bos indicus from High Altitude Areas of Uttarakhand State, India

Abstract

Toll-like receptors (TLRs) play a significant role in the modulation of innate immune system, and till date 10 TLR genes have been identified in bovines. TLR3, TLR7, TLR8, and TLR9 recognize pathogen-associated molecular patterns specific to viruses. The foremost aim of this work was to characterize the TLR7 gene, which mainly recognizes the ssRNA viruses. The complete ORF of the TLR7 gene (3.17 kb) was amplified, cloned and sequenced for analysis from local non-descript cattle (Bos indicus) reared in high altitude areas of temperate western Himalayan region. It revealed 98.9–99.6 % amino acid sequence identity with different breeds of cattle, and 87.1–98.9 % identity with other species (bubaline, equine, swine, ovine). Phylogenetic analysis of the hill cattle TLR7 showed clustering of sequences in a group and nearest common ancestry with bubaline (Bubalus bubalis; Murrah buffalo). Homology prediction of hill cattle TLR7 revealed highly conserved horseshoe shaped solenoid structure as found in other TLR structures. The structure consisted of 25 parallel β-strands, perpendicular to the solenoid axis and connected to each other by intervening loops. The hill cattle TLR7 showed unique substitutions at three amino acid positions compared to any other cattle breeds viz. Sahiwal, Red Sindhi, Gir, Kankrej, Hariana (K687 → Q, S731 → P, and Y890 → H). The substitution, S731 → P appeared to be critical, as the amino acid proline is involved in the formation of hinge or kink in a protein molecule.