9.B.352. The Mucin-like Protein (MLP) Family
Bombyx mori densovirus type 1 (BmDV) causes flacherie disease in silkworms. The nonsusceptibility to BmDV among certain silkworm strains is determined independently by two genes, nsd-1 and nid-1. Ito et al. 2018 isolated the nsd-1 gene and showed that it encodes a Bombyx-specific mucin-like glycoprotein with a single TMS. The NSD-1 protein was specifically expressed in the larval midgut epithelium, the known infection site of BmDV. Sequence analysis of the nsd-1 gene from 13 resistant and 12 susceptible strains suggested that a specific arginine residue in the extracellular tail of the NSD-1 protein was common among susceptible strains. Germline transformation of the susceptible-type nsd-1 (with a single nucleotide substitution) conferred susceptibility to resistant larvae, indicating that the + (nsd-1) gene is required for the susceptibility of B. mori larvae to BmDV, and this susceptibility is solely a result of the substitution of a single amino acid with arginine. Thus, a novel membrane-bound mucin-like protein functions as a cell-surface receptor for a densovirus (Ito et al. 2018). The N-termini of these proteins resemble glutamyl aminopeptidase-like isoform X2 of Papilio xuthus (XP_013180265).