A 35-KDA PROTEIN IS THE BASIC UNIT OF THE CORE FROM THE 2X10(4)-KDA AGGREGATION FACTOR RESPONSIBLE FOR SPECIES-SPECIFIC CELL-ADHESION IN THE MARINE SPONGE MICROCIONA-PROLIFERA

Dissociated sponge cells quickly reaggregate in a species-specific man ner, differentiate, and reconstruct tissue, providing a very handy sys tem to investigate the molecular basis of more complex intercellular r ecognition processes. Species specific cell adhesion in the marine spo nge Microciona prolifera is mediated by a supramolecular complex with a M(r) = 2 x 10(7), termed aggregation factor, Guanidinium hydrochlori de/cesium chloride dissociative gradients and rhodamine B isothiocyana te staining indicated the presence of several proteins with different degrees of glycosylation. Hyaluronate has been found to be associated with the aggregation factor. Chemical deglycosylation revealed a main component accounting for nearly 90% of the total protein. The cDNA-ded uced amino acid sequence predicts a 35-kDa protein (MAFp3), the first sponge aggregation factor core protein ever described, The open readin g frame is uninterrupted upstream from the amino terminus of the matur e protein, and the deduced amino acid sequence for this region has bee n found to contain a long stretch sharing homology with the Na+-Ca2+ e xchanger protein. A putative hyaluronic acid binding domain and severa l putative N- and O-glycosylation signals are present in MAFp3, as wel l as eight cysteines, some of them involved in intermolecular disulfid e bridges. Northern blot data suggest variable expression, and Souther n blot analysis reveals the presence of other related gene sequences. According to the respective molecular masses, one aggregation factor m olecule would contain about 300 MAFp3 units, suggesting that sponge ce ll adhesion might be based on the assembly of multiple small glycosyla ted protein subunits.