Cloning and functional characterization of a vertebrate low-density lipoprotein receptor homolog from eri silkmoth

receptor and belongs to the low-density lipoprotein receptor (LDLR) superfamily. It has a vital role in the uptake of lipophorin (Lp) into various tissues. Here we report the full length cloning and functional characterization of an LpR from eri silkmoth, Samia ricini. The full length cDNA of SrLpR7-1 is 4132 bp including an open reading frame (ORF) of 2595 bp. The deduced amino acid sequence revealed well structured ligand binding, epidermal growth factor, glycosylation, transmembrane and cytoplasmic domains. The ligand binding domain consisted of seven cysteine repeats instead of the common eight cysteine repeats indicating it as a homolog of human LDLR. We identified another splice variant, SrLpR7-2 with a deletion of 27 amino acids in the O-glycosylation domain. Apart from the fat body, both isoforms are expressed in ovary, brain and other tissues at different developmental stages of the silkworm. RNAi experiments did not show any marked effects except that the adult emergence was delayed compared to controls. In addition, the SrLpR7 cDNA was recombinantly expressed and ligand binding experiments confirmed that the receptor protein binds not only to SrLp but also to Bombyx mori Lp. Research Article