Sequence based structural characterization and genetic diversity analysis across coding and promoter regions of goat Toll-like receptor 5 gene

Abstract

The exploration of candidate immune response genes in goat may be vital in improving further our understanding about the species specific response to pathogens specifically among the ruminants. In this study, approximately 3.7 kb long genomic sequence of Toll-like receptor 5 (TLR5) covering the entire coding and 5'upstream regions of the gene, was characterized in the Indian goat breeds. Sequence analysis revealed a 2577-nucleotide long open reading frame (ORF) of goat TLR5, encoding 858 amino acids from single exon, similar to other ruminants. The domain structure analysis of goat TLR5 showed the presence of 13 leucine rich repeats (LRRs) in extracellular domain (amino acid position 1-634), single transmembrane domain (position 644-666), and a Toll/interleukin-1 receptor (position 692-837) in cytoplasmic domain, similar to other species. A total of 87 putative transcription factor binding sites were observed within the 5' upstream region of TLR5 gene in goat, 106 in cattle, and 103 in buffalo. Sixteen polymorphic sites were observed in goat TLR5 gene, out of which 10 non-synonymous SNPs were in the functionally important regions. However, none of the amino acid substitutions was found to be potentially damaging to the structure and function of the receptor protein. Further, one of the SNPs in the transmembrane region was genotyped by a TETRA-ARMS PCR in 444 goats of nine breeds from different geographical regions and having different utilities. A significant variation in allelic frequencies was observed across the milch and other types of goat breeds. The comparative modeling of goat TLR5 followed by molecular dynamics simulation gave an insight into its 3D structural arrangements. The molecular docking of Salmonella flagellin and TLR5 dimer elucidated LRRNT (N-terminal) to LRR4 as the key flagellin binding domains region in goat TLR5. The study shows that, although being highly conserved among the ruminants, comparatively high variations in goat TLR5 might give an opportunity to host for recognizing the wider spectrum of pathogens.

Keywords: Goat, Toll-like receptor 5; Leucine-rich repeats (LRR); Molecular docking; Molecular dynamics simulation; Polymorphism; Toll/IL-1 receptor (TIR) domain; Transcription factor binding sites.