The Gene Product of IMPG1 is the Glycoprotein SPACR, not an IPM Proteoglycan
From affinity purified SPACR we obtained seven peptides whose sequences reveal 100% identity to the deduced sequences in IMPG1 (accession number AF047492). The gene product of IMPG 1 is described as a chondroitin-6-sulfate proteoglycan. We report here that SPACR is the most prominent 147–150kD molecule present in the IPM. SPACR is not a chondroitin sulfate proteoglycan since it is not a product of chondroitinase ABC digestion and does not react with a highly specific chondroitin-6-sulfate antibody. Additionally, the deduced amino acid sequence of IMPG1 reveals no established glycosaminoglycan attachment site. We conclude that the glycoprotein SPACR is the gene product of IMPG1. SPACR is a heavily sialated glycoprotein containing both N- and O-linked glyconjugates. It is not the core protein of an IPM specific chondroitin sulfate proteoglycan.
KeywordsCore Protein Wheat Germ Agglutinin Human Retina Accession Number AF047492 Chondroitin Sulfate Proteoglycan
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