Physicochemical and functional characterization of the polymerization process of the Geodia cydonium lectin

Abstract

The extracellularly localized, galactose‐specific lectin from the sponge Geodia cydonium binds at one class of sites, 40 mol Ca2+/mol lectin with an association constant (Ka) of 0.3 × 106 M−1. Stoichiometric calculations reveal that in the extracellular milieu 22 mol Ca2+ (maximum) are complexed per mol lectin. Binding of Ca2‐ to the lectin increases its apparent Mr from 44000 to 56000 (electrophoretic determination) or from 36500 to 53500 (high‐pressure liquid gel chromatographical determination); the S20,w increases from 4.3 S to 4.5 S if Ca2‐ is added to the lectin. In the presence of Ca2+ the lectin undergoes a conformational change perhaps by expanding the carbohydrate side chains which are terminated by galactose. Subsequently the lectin molecules polymerize to large three‐dimensional clumps (diameter up to 8 μm). Turbidimetric studies reveal an inhibition of the lectin polymerization by lactose. The Ka of the lectin‐lectin polymerization rises from 0.9 × 106 M−1 to 14.0 × 106 M−1 after increasing the Ca2+ concentration (from 1 μM to 100 μM). Parallel with this increase in affinity, the Ka value of the lectin‐aggregation factor binding drops from 41.2 × 106 M−1 (1 μM Ca2+) to 1.3 × 106 M−1 (100 μM Ca2+). In the absence of Ca2+, the Geodia lectin forms 1–10‐μm two‐dimensional sheets in the presence of homologous glycoconjugates. Cell binding experiments with polyacrylamide gels, containing covalently bound galactose, show that both homologous (Geodia cydonium) and heterologous cells (L 5178y) bind with a higher affinity to the lectin‐polymer matrix than to the lectin‐monomer one. These data suggest that lectin‐polymer structures, together with lectin‐glycoconjugate associates, are components of the cell‐substrate adhesion system(s) of sponges in vivo.

Co-expression and Functional Interaction of Silicatein with Galectin

“…This lectin comprises, in contrast to galectin-1 from G. cydonium (35), not only two galactose-binding sites but also one hydrophobic region at its N terminus. It is important for the understanding of the silicatein function that S. domuncula galectin-2 is able to self-associate in the presence of Ca 2ϩ ; this property already has been described earlier for the G. cydonium galectin (41). Also in G. cydonium, galectin is a dominant protein in the mesohyl (41,43), which forms in the presence of Ca 2ϩ ions three-dimensional self-associates, with sizes of Ͼ1 m. Because the native S. domuncula galectin-2 is a glycoprotein, we assume that this self-association is due to the binding of the galactose-binding domain to the carbohydrate side chains within galectin-2, as shown for the G. cydonium galectin.…”

“…G. cydonium (35,41) and S. domuncula (42). In S. domuncula the differential display of transcripts revealed one dominant galectin, termed galectin-2.…”

Biochemical and biophysical characterization of collagens of marine sponge, Ircinia fusca (Porifera: Demospongiae: Irciniidae)

“…The existence of collagen in marine as well as freshwater sponges was first proved electron microscopically in 1980s [20,34]. Investigations regarding the fine structure and physicochemical properties of collagen of the marine sponge C. reniformis Nardo started with the studies by Garrone et al [35].…”

“…A modified procedure of Diehl-Seifert et al [20] was followed for the purification of functionally active collagens from I. fusca by gel filtration on a Sepharose 4B column (5 cm × 30 cm) using the 100 mM Tris-HCl buffer (pH 9.0) as eluant. Collagens of fibrillar and non-fibrillar nature were freed in the post column extractions, which were then characterized by microscopic and immunoblotting analyses.…”

Chemical modification of the lectin of the marine coral Gerardia savaglia by marine quinone avarone

“…16,17 Although additional evidence is necessary, the obtained results could indicate covalent modification of the lectins as a possible manner of action in these processes, essential for the survival of these sedentary organisms. Marine lectins are involved in cell recognition and aggregation and in the process of the elimination of foreign organisms.…”