A galectin links the aggregation factor to cells in the sponge (Geodia cydonium) system

Abstract

The cDNA for the full-length lectin from the marine sponge Geodia cydonium was cloned. Analysis of the deduced aa sequence revealed that this lectin belongs to the group of galectins. The full-length galectin, which was obtained also in a recombinant form, has an M(r) of 20,877; in the processed form it is a 15 kDa polypeptide. The enriched aggregation factor from G.cydonium also was determined to contain, besides minimal amounts of the galectin, a 140 kDa polypeptide which is involved in cell-cell adhesion. Monoclonal antibodies have been raised against this protein; Fab' fragments prepared from them abolished cell-cell reaggregation. Cell reaggregation experiments revealed that the aggregation factor is an essential component in the aggregation process but it requires likewise the presence of the galectin. Antibodies against the galectin blocked the aggregation factor-mediated cell adhesion. A plasma membrane component was identified (a 29 kDa polypeptide) which interacted with the aggregation factor in the presence of galectin; binding could be blocked both by antibodies against the galectin as well as against the aggregation factor. Immunohistochemical analysis revealed that spherulous cells contain the galectin but not the aggregation factor. By laser scanning microscopy, it is shown that both the aggregation factor and the galectin are located at the rim of the cells. From these data we conclude that the G.cydonium aggregation factor binds to the cells via a galectin bridge.

Emergence and Disappearance of an Immune Molecule, an Antimicrobial Lectin, in Basal Metazoa

“…System-Enzyme-linked immunosorbent assays were performed at 20°C as described (32). 96-well polystyrene plates were coated with LPS (10 g/ml) and incubated for 5 h. Excess proteinbinding sites on the microtiter plates were blocked with 3% bovine serum albumin and washed three times.…”

Molecular characterization of prostate carcinoma tumor antigen-1, PCTA-1, a human Galectin-8 related gene

“…Within the galectin gene family, further sub-classi®cation can be made by distinguishing between galectins containing a single carbohydrate recognition domain (CRD) termed the prototype galectins, a two CRD containing polypeptide where each domain is separated by a linker sequence called the tandem repeat galectins and a chimeric-type protein wherein an unrelated aminoterminal domain is linked to a CRD (Cooper and Barondes, 1999;. Galectins appear to have originated at a fairly early time during evolution since they occur in marine sponges and fungi (Arata et al, 1997;Cooper et al, 1997;Greenhalgh et al, 1999;Wagner-Hulsmann et al, 1996). Functionally, the galectins as a family have been associated with diverse phenomena in every cellular compartment, including cell surface or extracellular roles in adhesion (Inohara and Raz, 1995;Kaltner and Stierstorfer, 1998;Lotan et al, 1994), cell to cell recognition and signaling (Inohara and Raz, 1995), intracellular association with speci®c organelles and within the nucleus in association with components of the splicing machinery and with mRNA splicing (Dagher et al, 1995;Vyakarnam et al, 1997Vyakarnam et al, , 1998.…”

Lectins from Tropical Sponges

“…Therefore, lectins most likely represent an accessory protein acting as a linker between those elements. There is only one report in the literature that assigns a definitive role for a sponge lectin, the Geodia cydonium lectin, which may act as a bridge linking the aggregation factor to cells (39). G. cydonium is the most characterized sponge lectin to date (6, 33, 40 -42), and it has been included recently (3,(43)(44)(45)(46) in the Galectins family (47)(48)(49)(50)(51)(52), based on DNA sequence homology.…”