HIGH-AFFINITY BINDING AND OVERLAPPING LOCALIZATION OF NEUROCAN AND PHOSPHACAN PROTEIN-TYROSINE PHOSPHATASE-ZETA BETA WITH TENASCIN-R, AMPHOTERIN, AND THE HEPARIN-BINDING GROWTH-ASSOCIATED MOLECULE/
P. Milev et al., HIGH-AFFINITY BINDING AND OVERLAPPING LOCALIZATION OF NEUROCAN AND PHOSPHACAN PROTEIN-TYROSINE PHOSPHATASE-ZETA BETA WITH TENASCIN-R, AMPHOTERIN, AND THE HEPARIN-BINDING GROWTH-ASSOCIATED MOLECULE/, The Journal of biological chemistry, 273(12), 1998, pp. 6998-7005
We have studied the interactions of the nervous tissue-specific chondr
oitin sulfate proteoglycans neurocan and phosphacan with the extracell
ular matrix protein tenascin-a and two heparin-binding proteins, ampho
terin and the heparin-binding growth-associated molecule (HB-GAM), usi
ng a radioligand binding assay, Both proteoglycans show saturable, hig
h affinity binding to tenascin-R with apparent dissociation constants
in the 2-7 nM range, Binding is reversible, inhibited in the presence
of unlabeled proteoglycan, and increased by similar to 60% following c
hondroitinase treatment of the proteoglycans, indicating that the inte
ractions are mediated via the core (glyco)proteins rather than by the
glycosaminoglycan chains, which may in fact partially shield the bindi
ng sites, In contrast to their interactions with tenascin-C, in which
binding was decreased by similar to 75% in the absence of calcium, bin
ding of phosphacan to tenascin-R was not affected by the absence of di
valent cations in the binding buffer, although there was a small but s
ignificant decrease in the binding of neurocan, Neurocan and phosphaca
n are also high affinity ligands of amphoterin and HB-GAM (K-d = 0.3-8
nM), two heparin-binding proteins that are developmentally regulated
in brain and functionally involved in neurite outgrowth, The chondroit
in sulfate chains on neurocan and phosphacan account for at least 80%
of their binding to amphoterin and HB-GAM. The presence of amphoterin
also produces a 5-fold increase in phosphacan binding to the neural ce
ll adhesion molecule contactin, Immunocytochemical studies showed an o
verlapping localization of the proteoglycans and their ligands in the
embryonic and postnatal brain, retina, and spinal cord, These studies
have therefore revealed differences in the interactions of neurocan an
d phosphacan with the two major members of the tenascin family of extr
acellular matrix proteins, and also suggest that chondroitin sulfate p
roteoglycans play an important role in the binding and/or presentation
of differentiation factors in the developing central nervous system.