A switch in disulfide linkage during minicollagen assembly in Hydra nematocysts

The smallest known collagens with only 14 Gly-X-Y repeats referred to as mi nicollagens are the main constituents of the capsule wall of nematocysts. T hese are explosive organelles found in Hydra, jellyfish, corals and other C nidaria, Minicollagen-1 of Hydra recombinantly expressed in mammalian 293 c ells contains disulfide bonds within its N- and C-terminal Cys-rich domains but no interchain cross-links. It is soluble and self-associates through n on-covalent interactions to form 25-nm-long trimeric helical rod-like molec ules. We have used a polyclonal antibody prepared against the recombinant p rotein to follow the maturation of minicollagens from soluble precursors pr esent in the endoplasmic reticulum and post-Golgi vacuoles to the disulfide -linked insoluble assembly form of the wall. The switch from intra- to inte rmolecular disulfide bonds is associated with 'hardening' of the capsule wa ll and provides an explanation for its high tensile strength and elasticity . The process is comparable to disulfide reshuffling between the NC1 domain s of collagen IV in mammalian basement membranes.