Calcium-induced conformational transition of trout ependymins monitored by tryptophan fluorescence

Abstract

Ependymins are secretory, calcium-binding sialoproteins which are the predominant constituents of the cerebrospinal fluid of many teleost fish. A bound form of these regeneration-responsive glycoproteins is associated with collagen fibrils of the extracellular matrix. Here, the tryptophan fluorescence of ependymins was monitored at various Ca(2+) concentrations. Two distinct states were identified with a relatively sharp transition at about 1 mM Ca(2+). In agreement with previous circular dichroism measurements, this strongly supports the hypothesis that a calcium-induced conformational change is important for the interaction of ependymins with components of the extracellular matrix. Such interactions with constituents of various basal laminae would also explain the important roles of piscine ependymins as well as invertebrate and mammalian ependymin-related proteins for cell adhesion processes and cell migration.

Keywords: Ependymins; MERP; calcium binding; cell adhesion molecule; extracellular matrix; learning and memory.; tryptophan fluorescence.

Fig. (1)

Fluorescence spectrum of FPLC-purified ependymins from the rainbow trout. Shown is the relative emission fluorescence of trout ependymins (180 µg/ml) between 300 and 420 nm (F_rel, in arbitrary units; excitation at 295 nm) at 10 mM Ca²⁺ and after complexation with EDTA.

Fig. (2)

Tryptophan fluorescence of FPLC-purified ependymins from the rainbow trout. Shown is the relative emission fluorescence of trout ependymins (191 µg/ml) at 335 nm (F_rel, in arbitrary units; excitation at 295 nm) as a function of the Ca²⁺ concentration. Each point represents the mean of three measurements.