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J Biol Chem, Vol. 275, Issue 10, 6945-6955, March 10, 2000
SPACRCAN, a Novel Human Interphotoreceptor Matrix
Hyaluronan-binding Proteoglycan Synthesized by Photoreceptors and
Pinealocytes*
Shreeta
Acharya §¶,
Victoria C.
Foletta§ ,
Jung Wha
Lee**,
Mary E.
Rayborn ,
Ignacio R.
Rodriguez**,
W. Scott
Young III , and
Joe G.
Hollyfield 
From the Cole Eye Institute, The Cleveland Clinic
Foundation, Cleveland, Ohio 44195, The National Institute
of Mental Health, and ** The National Eye Institute, The National
Institutes of Health, Bethesda, Maryland 20892
The interphotoreceptor matrix is a unique
extracellular complex occupying the interface between photoreceptors
and the retinal pigment epithelium in the fundus of the eye. Because of
the putative supportive role in photoreceptor maintenance, it is likely
that constituent molecules play key roles in photoreceptor function and
may be targets for inherited retinal disease. In this study we identify
and characterize SPACRCAN, a novel chondroitin proteoglycan in this
matrix. SPACRCAN was cloned from a human retinal cDNA library
and the gene localized to chromosome 3q11.2. Analysis of
SPACRCAN mRNA and protein revealed that SPACRCAN is expressed exclusively by photoreceptors and pinealocytes. SPACRCAN synthesized by
photoreceptors is localized to the interphotoreceptor matrix where it
surrounds both rods and cones. The functional protein contains 1160 amino acids with a large central mucin domain, three consensus sites
for glycosaminoglycan attachment, two epidermal growth
factor-like repeats, a putative hyaluronan-binding motif, and a
potential transmembrane domain near the C-terminal. Lectin and Western
blotting indicate an Mr around 400,000 before
and 230,000 after chondroitinase ABC digestion. Removal of
N- and O-linked oligosaccharides reduces the
Mr to approximately 160,000, suggesting that
approximately 60% of the mass of SPACRCAN is carbohydrate. Finally, we
demonstrate that SPACRCAN binds hyaluronan and propose that
associations between SPACRCAN and hyaluronan may be involved in
organization of the insoluble interphotoreceptor matrix, particularly as SPACRCAN is the major proteoglycan present in this matrix.
*
This work was supported by Grant EY 02362 from the National
Institutes of Health, The Foundation Fighting Blindness, Hunt Valley,
MD, The Retina Research Foundation, Houston, TX, and funds from The
Cleveland Clinic Foundation.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) AF157624.
§
Contributed equally to this analysis.
¶
Recipient of an award from the Knights Templar Eye Foundation,
Chicago, Il.

Recipient of the 1999 Ocular Cell and Molecular Biology Prize
from Allergan Laboratory for career contributions to vision research.
To whom correspondence should be addressed. Tel.: 216-445-3252; Fax:
216-445-3670.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2000 by the American Society for Biochemistry and Molecular Biology.
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