Circular proteoglycans from sponges: first members of the spongican family

Abstract

Species-specific cell adhesion in marine sponges is mediated by a new family of modular proteoglycans whose general supramolecular structure resembles that of hyalectans. However, neither their protein nor their glycan moieties have significant sequence homology to other proteoglycans, despite having protein subunits equivalent to link proteins and to proteoglycan monomer core proteins, and glycan subunits equivalent to hyaluronan and to the glycosaminoglycans of hyalectans. In some species, these molecular components are assembled into a structure with a circular core formed by the link protein- and hyaluronan-like subunits. Besides their involvement in cell adhesion, these sponge proteoglycans, for which we propose the term spongicans, participate in signal transduction processes and are suspected to play a role in sponge self-nonself recognition. Their in vivo roles and the mild methods used to purify large amounts of functionally active spongicans make them ideal models to study the functions and possible new applications of proteoglycans in biomedical research.

Carbohydrate-Carbohydrate Interactions Mediated by Sulfate Esters and Calcium Provide the Cell Adhesion Required for the Emergence of Early Metazoans

“…The data used to calculate the F max were restricted to the last peak of the force curves to ensure that only single molecule self-interaction forces were taken into consideration. The striking supramolecular similarities with MAF clearly place DAF within the family of circular proteoglycans from sponges, the spongicans (15). This finding is consistent with the phylogenetic kinship of D. anchorata and M. prolifera; both of these species belong to the sponge order Ceractinomorpha (38).…”

“…Sites-Images of DAF acquired via high resolution AFM revealed a proteoglycan remarkably similar to the AF of the sponge M. prolifera (MAF) described elsewhere (8,14,15), which enabled us to trace parallels between their structures, compositions, and chemical behaviors. DAF has a sunburst-shaped core constructed by a ring, ϳ130 nm across, and radiating arms up to 190 nm in length (Fig.…”

“…This model mimics the conspicuous aggregation process whereby dissociated sponge cells undergo when kept in culture (15). Beads coated with native and carboxyl-reduced DaSP and incubated in CMFTSW supplemented with 10 mM CaCl 2 (Fig.…”

“…The structures of AFs resemble those of aggrecans: large, extracellular membrane-bound, aggregating, and modular proteoglycans (15). In the marine sponge Microciona prolifera the AF is constructed by a protein core attached to two different carbohydrate units: a small 6-kDa glycan that mediates the interaction of the AF with putative receptors present in the cell membrane and a larger 200-kDa sulfated polysaccharide, which binds homophilically with identical units on the AFs of adjacent cells (13)(14)(15)(16).…”

Adhesion forces in the self-recognition of oligosaccharide epitopes of the proteoglycan aggregation factor of the marine sponge Microciona prolifera

“…Later studies revealed that the speciesspecific cell aggregation of the marine sponge Microciona prolifera is mediated by a proteoglycan-like aggregation factor (MAF). Hereby, the N-glycans of two functional domains of MAF, MAFp4 and MAFp3, play an essential role: (i) the MAFp4-bound 6-kDa glycan (known as g-6), which in a Ca 2+ -independent way adheres to cell surface receptors, and (ii) the MAFp3-bound 200-kDa glycan (known as g-200), which promotes cell adhesion via a Ca 2+ -dependent self-association process [2,3]. Specific monoclonal antibodies against purified MAF, called Block 1 and Block 2, could inhibit the Ca 2+ -dependent self-association process without interfering with the cell-binding activity.…”