Molecular cloning of goat Mannose 6-phosphate receptors, MPR 300 and 46

Mannose 6-phosphate receptor proteins (MPR 300 and 46) are type 1 transmembrane glycoproteins that mediate transport of lysosomal enzymes to lysosomes. In a recent study we have purified both receptors from goat liver and raised antibodies. An ELISA method was developed that allowed quantification of both receptors in different tissues of goat and chicken and an immuno-affinity method was also developed to purify the receptors. In the present study to understand the structural similarities of the goat receptors to other known receptor proteins, we have prepared cDNA clones for both receptors by RT-PCR approach. A partial cDNA clone (1.368 kb) for the MPR 300 protein, and a full length cDNA clone (0.84 kb) for the MPR 46 protein were obtained. MPR 300 exhibits typical conserved cassette structure in the amino terminal domain similar to other known vertebrate MPR proteins with the conserved cysteine residues and the ligand binding arginine residue in the third domain. MPR 46 exhibits high degree of sequence homology to other known MPR proteins with the conserved cysteine residues, the transmembrane domain and the cytoplasmic tail. mRNA transcript size for both receptors were comparable with that of other vertebrates.