SPACR, a novel interphotoreceptor matrix glycoprotein in human retina that interacts with hyaluronan.
SPACR (sialoprotein associated with cones and rods), is the major 147-150-kDa glycoprotein present in the insoluble interphotoreceptor matrix of the human retina. Immunocytochemistry localizes SPACR to the matrix surrounding rods and cones (Acharya, S., Rayborn, M. E., and Hollyfield, J. G. (1998) Glycobiology 8, 997-1006). From affinity-purified SPACR, we obtained seven peptide sequences showing 100% identity to the deduced sequence of IMPG1, a purported chondroitin 6-sulfate proteoglycan core protein, which binds peanut agglutinin and is localized to the interphotoreceptor matrix. We show here that SPACR is the most prominent 147-150-kDa band present in the interphotoreceptor matrix and is the gene product of IMPG1. SPACR is not a chondroitin sulfate proteoglycan, since it is not a product of chondroitinase ABC digestion and does not react to a specific antibody for chondroitin 6-sulfate proteoglycan. Moreover, the deduced amino acid sequence reveals no established glycosaminoglycan attachment site. One hyaluronan binding motif is present in the predicted sequence of SPACR. We present evidence that SPACR has a functional hyaluronan binding domain, suggesting that interactions between SPACR and hyaluronan may serve to form the basic macromolecular scaffold, which comprises the insoluble interphotoreceptor matrix.
Acharya
S
S
The Eye Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Rodriguez
I R
IR
Moreira
E F
EF
Midura
R J
RJ
Misono
K
K
Todres
E
E
Hollyfield
J G
JG
D000595:Amino Acid Sequence; D016326:Extracellular Matrix Proteins / Q000737:chemistry* / Q000378:metabolism*; D005136:Eye Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006820:Hyaluronic Acid / Q000378:metabolism*; D037102:Lectins / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D020419:Photoreceptor Cells, Vertebrate / Q000737:chemistry*; D011485:Protein Binding; D011509:Proteoglycans; D012160:Retina / Q000737:chemistry*; D017421:Sequence Analysis
D016326:Extracellular Matrix Proteins; D005136:Eye Proteins; C486428:IMPG1 protein, human; D037102:Lectins; D010446:Peptide Fragments; D011509:Proteoglycans; D006820:Hyaluronic Acid