Structural Prediction and Antigenic Characterization of Recombinant Nucleocapsid Protein (p14) of Small Ruminant Lentivirus.

Small ruminant lentivirus (SRLV) infects goats and sheep of all breeds and ages worldwide. There are no current records regarding the three-dimensional structure or antigenic capacity of the nucleocapsid protein p14 of FESC-752 Mexican strain. The antigenic structure of p14 protein of a B1 genotype was predicted. cDNA from FESC-752 was used to overexpress the recombinant SRLV-rp14 protein. Then, its antigenicity was verified in vitro by evaluating plasma samples from goats and sheep naturally infected with SRLV. Antigenicity prediction showed a "horseshoe"-type structure shared by different lentiviruses and five epitopes distributed throughout the p14 surface regions where they coincide suggesting conserved epitopes in the zinc-finger structures of the nucleoproteins of the SRLV, Human Immunodeficiency Virus (HIV-1), and Feline Immunodeficiency virus (FIV) retroviruses. Multi-species molecular docking showed a notable structural convergence where caprine, bovine, murine, and human immunoglobulins target a predictive 23 amino acid epitope (residues 41-64) within the core zinc-finger region. Furthermore, CABS docking simulations predicted that p14-derived peptides preferentially bind within the antigen-presenting cleft of both caprine and bovine major histocompatibility complex class I (MHC-I) molecules. The stability of these immunological complexes is mediated by dense networks of hydrophobic interactions and highly conserved aromatic anchoring residues. Antigenicity analysis revealed that 78.7% of samples from naturally infected goats showed immunoreactivity toward SRLV-rp14 and the predictive evidence that p14 can simultaneously stimulate both humoral and cellular pathways makes it a strategic candidate for the design of next-generation vaccines aimed at controlling lentiviruses in small ruminants.