Amassin, an olfactomedin protein, mediates the massive intercellular adhesion of sea urchin coelomocytes.
Sea urchins have a fluid-filled body cavity, the coelom, containing four types of immunocytes called coelomocytes. Within minutes after coelomic fluid is removed from the body cavity, a massive cell-cell adhesion of coelomocytes occurs. This event is referred to as clotting. Clotting is thought to be a defense mechanism against loss of coelomic fluid if the body wall is punctured, and it may also function in the cellular encapsulation of foreign material and microbes. Here we show that this intercoelomocyte adhesion is mediated by amassin, a coelomic plasma protein with a relative molecular mass (Mr) of 75 kD. Amassin forms large disulfide-bonded aggregates that adhere coelomocytes to each other. One half of the amassin protein comprises an olfactomedin (OLF) domain. Structural predictions show that amassin and other OLF domain-containing vertebrate proteins share a common architecture. This suggests that other proteins of the OLF family may function in intercellular adhesion. These findings are the first to demonstrate a function for a protein of the OLF family.
Hillier
Brian J
BJ
Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA. bhillier@ucsd.edu
Vacquier
Victor D
VD
D000595:Amino Acid Sequence; D000818:Animals; D001826:Body Fluids / Q000737:chemistry*; D002448:Cell Adhesion / Q000502:physiology*; D004220:Disulfides; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000378:metabolism; D012617:Sea Urchins / Q000166:cytology* / Q000502:physiology*; D016415:Sequence Alignment
D004220:Disulfides; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D046911:Macromolecular Substances; D011994:Recombinant Proteins; C081451:olfactomedin