Protein-induced, previously unidentified twin form of calcite
- Departments of †Materials Engineering and
- §Chemistry, Technion–Israel Institute of Technology, Haifa 32000, Israel; and
- ¶Laboratoire de Biogéosciences, Unité Mixte de Recherche 5561, Université de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France
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Edited by Joanna Aizenberg, Lucent, Murray Hill, NJ, and accepted by the Editorial Board March 14, 2007 (received for review September 28, 2006)
Abstract
Using single-crystal x-ray diffraction, we found a formerly unknown twin form in calcite crystals grown from solution to which a mollusc shell-derived 17-kDa protein, Caspartin, was added. This intracrystalline protein was extracted from the calcitic prisms of the Pinna nobilis shells. The observed twin form is characterized by the twinning plane of the (108)-type, which is in addition to the known four twin laws of calcite identified during 150 years of investigations. The established twin forms in calcite have twinning planes of the (001)-, (012)-, (104)-, and (018)-types. Our discovery provides additional evidence on the crucial role of biological macromolecules in biomineralization.
Footnotes
- ‡To whom correspondence should be addressed. E-mail: bpokroy{at}tx.technion.ac.il
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Author contributions: B.P., N.A., and E.Z. designed research; B.P. and M.K. performed research; F.M. and N.A. contributed new reagents/analytic tools; B.P., M.K., and E.Z. analyzed data; and B.P. and E.Z. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission. J.A. is a guest editor invited by the Editorial Board.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0608584104/DC1.
- © 2007 by The National Academy of Sciences of the USA
