DIFFERENTIAL TARGETING OF CLOSELY-RELATED ECM GLYCOPROTEINS - THE PHEROPHORIN FAMILY FROM VOLVOX

The alga Volvox carteri represents one of the simplest multicellular o rganisms. Its extracellular matrix (ECM) is modified under development al control, e.g. under the influence of the sex-inducing pheromone tha t triggers development of males and females at a concentration below 1 0(-16) M. A novel ECM glycoprotein (pherophorin-S) synthesized in resp onse to this pheromone was identified and characterized. Although bein g a typical member of the pherophorins, which are identified by a C-te rminal domain with sequence homology to the sex-inducing pheromone, ph erophorin-S exhibits a completely novel set of properties. In contrast to the other members of the family, which are found as part of the in soluble ECM structures of the cellular zone, pherophorin-S is targeted to the cell-free interior of the spherical organism and remains in a soluble state. A main structural difference is the presence of a polyh ydroxyproline spacer in pherophorin-S that is linked to a saccharide c ontaining a phosphodiester bridge between two arabinose residues. Sequ ence comparisons indicate that the self-assembling proteins that creat e the main parts of the complex Volvox ECM have evolved from a common ancestral gene.