Molecular characterization of the VLDL receptor homolog mediating binding of lipophorin in oocyte of the mosquito Aedes aegypti

Lipophorin (Lp) functions as a yolk protein precursor in the mosquito Aedes aegypti and it is internalized via receptor-mediated endocytosis (Insect B iochem. Mel. Biol., 30 (2000) 1161). We cloned and molecularly characterize d a putative mosquito ovarian lipophorin receptor (AaLpRov) cDNA. The cDNA has a length of 3468 bp coding for a 1156-residue protein with a predicted molecular mass of 128.9 kDa. The deduced amino acid sequence of the cDNA re vealed that it encodes a protein homolog of the LDL receptor superfamily, a nd that it harbors eight cysteine-rich ligand binding repeats at the N-term inus like vertebrate VLDL receptors. The deduced amino acid sequence of thi s mosquito ovarian receptor is most similar to that of the locust lipophori n receptor (LmLpR) (64.3%), and is only distantly related to the mosquito v itellogenin receptor (VgR) (18.3%), another ovarian LDLR homolog with a dif ferent ligand. The AaLpRov cDNA was expressed in a TnT(R) Coupled Reticuloc yte Lysate system, and coimmunoprecipitation experiments confirmed that the receptor protein specifically binds Lp. Developmental expression profiles clearly showed that AaLpRov transcripts are present in the vitellogenic ova ry, with peak expression at 24-36 h post blood meal. In situ hybridization indicated that AaLpRov transcripts are present only in female germ line cel ls. Distance-based phylogenetic analyses suggest that the insect LpR and ve rtebrate LDL/VLDL receptor lineages separated after divergence from the ins ect VgR lineage. (C) 2001 Elsevier Science Ltd. All rights reserved.