Identification and characterization of a Penaeus monodon lymphoid cell-expressed receptor for the yellow head virus

The yellow head virus is a positive-sense, single-stranded RNA virus that causes significant mortality in farmed penaeid shrimp. This study sought to isolate and characterize the receptor protein used by the virus to gain entry into Penaeus monodon Oka (lymphoid) organ cells, a primary target of yellow head virus infections. Virus overlay protein binding assay on Oka organ membrane preparations identified a 65-kDa protein, and antibodies raised against this protein inhibited virus entry in primary Oka cell cultures by approximately 80%. N-terminal sequence analysis of the 65-kDa protein generated a 17-amino acid peptide fragment which was used to design degenerate primers that amplified a 1.5-kbp product from Oka organ total RNA, which was cloned and sequenced. Northern analysis and PCR were used to confirm a single RNA transcript that was expressed in most tissues. Subsequently, the mature cDNA was recloned and the expressed protein shown to cross-react with the antibody raised against the original virus binding band. Down regulation of the message through double-stranded RNA-mediated RNA interference silencing resulted in the complete inhibition of virus entry. While the identity of the clone remains unknown, it nevertheless represents the first invertebrate Nidovirus receptor isolated to date.