SPACR, a Novel Interphotoreceptor Matrix Glycoprotein in Human Retina That Interacts with Hyaluronan

doi:10.1074/jbc.273.47.31599

SPACR, a Novel Interphotoreceptor Matrix Glycoprotein in Human Retina That Interacts with Hyaluronan*

From ^‡The Eye Institute and ^¶The Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195 and ^§NEI, National Institutes of Health, Bethesda, Maryland 20892

Abstract

SPACR (sialoproteinassociated 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.

Footnotes

↵* This work was supported by National Institutes of Health Grant EY 02362 and grants from the Foundation Fighting Blindness (Hunt Valley, MD), the Retina Research Foundation (Houston, TX), and funds from the Cleveland Clinic Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Abbreviations:

IPM

interphotoreceptor matrix

IMPG1

interphotoreceptor matrix proteoglycan 1

BSA

bovine serum albumin

CPC

cetylpyridinium chloride

EGF

epidermal growth factor

GAG

glycosaminoglycan

HA

hyaluronan

PAGE

polyacrylamide gel electrophoresis

PNA

peanut agglutinin

RHAMM

receptor for hyaluronan mediated motility

SPACR

sialoprotein associated with cones and rods

TBS

Tris-buffered saline

3B3

chondroitin 6-sulfate Δ-disaccharide-specific antibody

WGA

wheat germ agglutinin

MOPS

4-morpholinepropanesulfonic acid.
- Received August 27, 1998.
- Revision received September 10, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.