Epitope mapping of Canine distemper virus phosphoprotein by monoclonal antibodies

Identification of Linear B-Cell Epitopes on Hemagglutinin Protein of Canine Distemper Virus Using Two Monoclonal Antibodies

Canine distemper virus (CDV) belongs to the Morbillivirus genus of the Paramyxoviridae family, which causes a threat to the domestic dog and fur-animal industry. Hemagglutinin protein is a major membrane protein of the vital molecular factor in CDV tropism, also known to induce hosts to produce neutralizing antibodies. In the current study, we prepared two monoclonal antibodies, 1A5 and 2B8, against the H protein of the CDV-PS strain. A series of partially overlapping synthetic peptides covering the hemagglutinin protein (amino acids 50–204) were screened to define the linear epitope identified by 1A5 and 2B8 mAbs. ¹²⁰QKTNFFNPNREFDFR¹³⁴ (F8) and ¹⁷⁸ARGDIFPPY¹⁸⁶ (F14-1) are minimal linear epitopes recognized by 1A5 and 2B8 mAbs, respectively. Further investigations revealed that F8 is conserved in different CDV strains; however, F14-1 contains mutant residues 178, 179, and 180. The epitopes F8 and F14-1 localized at the surface of hemagglutinin protein in a three-dimensional (3D) structure. CDV-infected dog serum can also recognize the identified B-cell epitopes.

Development of CDV-specific monoclonal antibodies for differentiation of variable epitopes of nucleocapsid protein

The highly contagious canine distemper viruses (CDVs) are still a major threat to a wide range of natural susceptible hosts. The nucleocapsid (N) protein plays various roles in the virus-induced immune response. But precise mapping of epitopes and antigenic variations in N protein of CDV are still scant. In this study, two monoclonal antibodies (MAbs), designated as F8N and G3N, against the N protein of CDV were generated and characterized. The epitopes recognized by the two MAbs were mapped by truncated N protein fragments expressed in E.coli based on western blotting. The 470ESRYDTQ476 and 385GITKEEAQL393 were identified as the minimal linear epitopes recognized by F8N and G3N, respectively. The amino acid residues of the epitope (385-393aa) were highly conserved in a variety of CDV strains from the databases as well as five CDV strains in this study, indicating that MAb G3N can detect various CDV strains. However, MAb F8N was found not to react with an older CDV 851 strain of the five CDV strains due to both of two amino substitution (S471P and Y473H) in the epitope, whereas either single mutant S471P or Y473H did not eliminate the binding of F8N. Further, the variable epitopes existed in the N protein of six CDV strains resembling CDV3 in phylogenic tree by alignment with sequences from the databases. This is the first record of a precise epitope affecting antigenity of N protein of CDV. These results may facilitate future investigations into the function of NP of CDV and diagnostic methods for CDV infection.

Phosphorylation of measles virus phosphoprotein at S86 and/or S151 downregulates viral transcriptional activity

Measles virus phosphoprotein (P protein) is a cofactor of the viral RNA polymerase (L protein) that associates with the nucleoprotein-RNA complex to support viral transcription and replication. Here, we report a significant inverse correlation between the phosphorylation level of MV-P protein and viral transcriptional activity. Upregulation of P protein phosphorylation resulted in reduction of viral transcription. Additionally, we found that strong phosphorylation at S86 and S151 of P protein, which may be generally prevented by association with nucleoprotein, downregulates the viral transcriptional activity. These findings suggest that P protein is involved in regulation of viral transcription through changes in its phosphorylation status.