Biochem Cell Biol 2007 Oct 01;855:552-62. doi: 10.1139/o07-055.

Structural features and functional domains of amassin-1, a cell-binding olfactomedin protein.

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Amassin-1 mediates a rapid cell adhesion that tightly adheres sea urchin coelomocytes (body cavity immunocytes) together. Three major structural regions exist in amassin-1: a short beta region, 3 coiled coils, and an olfactomedin domain. Amassin-1 contains 8 disulfide-bonded cysteines that, upon reduction, render it inactive. Truncated forms of recombinant amassin-1 were expressed and purified from Pichia pastoris and their disulfide bonding and biological activities investigated. Expressed alone, the olfactomedin domain contained 2 intramolecular disulfide bonds, existed in a monomeric state, and inhibited amassin-1-mediated clotting of coelomocytes by a calcium-dependent cell-binding activity. The N-terminal beta region, containing 3 cysteines, was not required for clotting activity. The coiled coils may dimerize amassin-1 in a parallel orientation through a homodimerizing disulfide bond. Neither amassin-1 fragments that were disulfide-linked as dimers or that were engineered to exist as dimers induced coelomocytes clotting. Clotting required higher multimeric states of amassin-1, possibly tetramers, which occurred through the N-terminal beta region and (or) the first segment of coiled coils.

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???displayArticle.link??? Biochem Cell Biol
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Genes referenced: LOC100887844 LOC115919910 olfm1b
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