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The nematocyst capsules of the cnidarians are specialized explosive organelles that withstand high osmotic pressures of 15 MPa (150 bar). A tight disulfide network involving cysteine-rich capsule wall proteins, like minicollagens and nematocyst outer wall antigen, characterizes their molecular composition. | iFEBS Journal Structure function analysis of spinalin a spine protein of Hydra nematocysts imnn I I o 11 e o m1 I n m IH 1 f h o rlo to Fa I icot 1 A riol I I le in1 IÍÌ mon Fnnol1 o II HUI in ciioLciii u oiy o tcicic III Iziiaiione rauoci Miivi LusLiy juiycn Liiyci Thomas W. Holstein2 and Suat Ozbek2 1 Department of BiophysicalChemistry Biozentrum University of Basel Switzerland 2 Institute for Molecular Evolution and Genomics Im Neuenheimer Feld Heidelberg Germany Correspondence S. Ozbek Institute for Molecular Evolution and Genomics Im Neuenheimer Feld 230 69130 Heidelberg Germany Fax 49 6221 545678 Tel 49 6221 545638 E-mail soezbek@zoo.uni-heidelberg.de Received 18 April2006 accepted 18 May 2006 doi 10.1111 j.1742-4658.2006.05331.x The nematocyst capsules of the cnidarians are specialized explosive organelles that withstand high osmotic pressures of w 15 MPa 150 bar . A tight disulfide network involving cysteine-rich capsule wall proteins like minicollagens and nematocyst outer wall antigen characterizes their molecular composition. Nematocyst discharge leads to the expulsion of a long inverted tubule that was coiled inside the capsule matrix before activation. Spinalin has been characterized as a glycine-rich histidine-rich protein associated with spine structures on the surface of everted tubules. Here we show that full-length Hydra spinalin can be expressed recombinantly in HEK293 cells and has the property to form disulfide-linked oligomers reflecting its state in mature capsules. Furthermore spinalin showed a high tendency to associate into dimers in vitro and in vivo. Our data which show incomplete disulfide connectivity in recombinant spinalin suggest a possible mechanism by which the spine structure may be linked to the overall capsule polymer. Nematocytes are specialized cells in the phylum Cnid-aria harboring unique organelles called nematocysts. Nematocysts serve different functions such as capture of prey defense and locomotion 1 . Despite the wide
