First published online January 18, 2008
Journal of Experimental Biology 211, 300-309 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.008193
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Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellid Monorhaphis chuni

Werner E. G. Müller1,*, Alexandra Boreiko1,{dagger}, Ute Schloßmacher1,{dagger}, Xiaohong Wang2, Carsten Eckert1,3, Klaus Kropf1, Jinhe Li4 and Heinz C. Schröder1

1 Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, D-55099 Mainz, Germany
2 National Research Center for Geoanalysis, 26 Baiwanzhuang Dajie, CHN-100037 Beijing, People's Republic of China
3 Museum für Naturkunde, Institut für Systematische Zoologie, Invalidenstraße 43, D-10155 Berlin, Germany
4 Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, CHN-266071 Qingdao, People's Republic of China

* Author for correspondence (e-mail: wmueller{at}uni-mainz.de)

Accepted 12 November 2007

Silicateins, members of the cathepsin L family, are enzymes that have been shown to be involved in the biosynthesis/condensation of biosilica in spicules from Demospongiae (phylum Porifera), e.g. Tethya aurantium and Suberites domuncula. The class Hexactinellida also forms spicules from this inorganic material. This class of sponges includes species that form the largest biogenic silica structures on earth. The giant basal spicules from the hexactinellids Monorhaphis chuni and Monorhaphis intermedia can reach lengths of up to 3 m and diameters of 10 mm. The giant spicules as well as the tauactines consist of a biosilica shell that surrounds the axial canal, which harbours the axial filament, in regular concentric, lamellar layers, suggesting an appositional growth of the spicules. The lamellae contain 27 kDa proteins, which undergo post-translational modification (phosphorylation), while total spicule extracts contain additional 70 kDa proteins. The 27 kDa proteins cross-reacted with anti-silicatein antibodies. The extracts of spicules from the hexactinellid Monorhaphis displayed proteolytic activity like the silicateins from the demosponge S. domuncula. Since the proteolytic activity in spicule extracts from both classes of sponge could be sensitively inhibited by E-64 (a specific cysteine proteinase inhibitor), we used a labelled E-64 sample as a probe to identify the protein that bound to this inhibitor on a blot. The experiments revealed that the labelled E-64 selectively recognized the 27 kDa protein. Our data strongly suggest that silicatein(-related) molecules are also present in Hexactinellida. These new results are considered to also be of impact for applied biotechnological studies.

Key words: sponges, Monorhaphis chuni, spicules, biosilica, silicatein-related protein


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