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First published online April 18, 2006
Journal of Experimental Biology 209, 1594-1602 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02178

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Tensilin-like stiffening protein from Holothuria leucospilota does not induce the stiffest state of catch connective tissue

Masaki Tamori^1,*, Akira Yamada², Naoto Nishida¹, Yumiko Motobayashi¹, Kazuhiro Oiwa² and Tatsuo Motokawa¹

¹ W3-42, Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro-ku, Tokyo 152-8551, Japan
² Kansai Advanced Research Center, National Institute of Information and Communications Technology, Kobe 651-2492, Japan

^* Author for correspondence (e-mail: mtamori{at}bio.titech.ac.jp)

Accepted 16 February 2006

The dermis of sea cucumbers is a catch connective tissue or mutable connective tissue that exhibits large changes in mechanical properties. A stiffening protein, tensilin, has been isolated from the sea cucumber Cucumaria frondosa. We purified a similar protein, H-tensilin, from Holothuria leucospilota, which belongs to a different family to C. frondosa. H-tensilin appeared as a single band with an apparent molecular mass of 34 kDa on SDS-PAGE. No sugar chain was detected. Tryptic fragments of the protein had homology to known tensilin. H-tensilin aggregated isolated collagen fibrils in vitro in a buffer containing 0.5 mol l^–1 NaCl with or without 10 mmol l^–1 Ca²⁺. The activity of H-tensilin was quantitatively studied by dynamic mechanical tests on the isolated dermis. H-tensilin increased stiffness of the dermis in the soft state, induced by Ca²⁺-free artificial seawater, to a level comparable to that of the standard state, which was the state found in the dermis rested in artificial seawater with normal ionic condition. H-tensilin decreased the energy dissipation ratio of the soft dermis to a level comparable to that of the standard state. When H-tensilin was applied on the dermis in the standard state, it did not alter stiffness nor dissipation ratio. The subsequent application of artificial seawater in which the potassium concentration was raised to 100 mmol l^–1 increased stiffness by one order of magnitude. These findings suggest that H-tensilin is involved in the changes from the soft state to the standard state and that some stiffening factors other than tensilin are necessary for the changes from the standard to the stiff state.

Key words: catch connective tissue, mutable connective tissue, stiffness, echinoderm, sea cucumber, tensilin

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