CALCIUM-BINDING TO SIALIC ACIDS AND ITS EFFECT ON THE CONFORMATION OFEPENDYMINS

Soluble ependymins form the predominant protein constituents in the ce rebrospinal fluid from many orders of teleost fish. Furthermore, these glycoproteins also exist in a bound form associated with the extracel lular matrix. Ependymins are synthesized in meningeal fibroblasts. In goldfish, their synthesis is increased during the regeneration of the optic nerve and they share several characteristics with molecules invo lved in cell contact phenomena. In this study, we show by a calcium ov erlay technique that ependymins from goldfish and rainbow trout are ab le to bind Ca-45(2+). However, nearly all of this Ca2+-binding capacit y is lost after digestion with sialidase. Furthermore, circular-dichro ism spectra from FPLC-purified rainbow trout ependymins have been reco rded in the presence and absence of Ca2+. Below 250 nm, the CD spectru m showed a characteristic minimum of ellipticity at 217 nm typical of beta structures. This signal is independent of the Ca2+ concentration. In contrast, the complex signal at 250-310 nm mainly decreased with i ncreasing Ca2+ concentration indicating changes in the environment of aromatic side chains.