Isolation of a sponge-derived extracellular matrix adhesion protein

The development of stable intercellular adhesions in the animal kingdom permitted the evolution of the metazoans, of which the sponges are primitive examples. Intercellular adhesion in these simple animals is mediated by a high affinity interaction between the sponge cell surface and aggregation factor, a 2 x 10(7)-Da proteoglycan that is one of the major components of the sponge extracellular matrix. This report describes a sponge cell surface and extracellular matrix ligand for the sponge proteoglycan, aggregation factor. The 210-kDa protein binds aggregation factor proteoglycan with high affinity (Kd = 7 x 10(-9) M). Importantly, in soluble form, it also inhibits aggregation factor-mediated cell adhesion. This glycoprotein is expressed on the sponge cell surface and within the extracellular matrix. This novel sponge extracellular matrix protein may represent a primitive antecedent of the extracellular matrix adhesion proteins of higher organisms.