Structure of the nacreous organic matrix of a bivalve mollusk shell examined in the hydrated state using Cryo-TEM

Yael Levi-Kalisman*, Giuseppe Falini, Lia Addadi, Steve Weiner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

460 Scopus citations

Abstract

During mollusk shell formation, the mineral phase forms within an organic matrix composed of β-chitin, silk-like proteins, and acidic glycoproteins rich in aspartic acid. The matrix is widely assumed to play an important role in controlling mineralization. Thus, understanding its structure is of prime importance. Cryo-transmission electron microscopy (Cryo-TEM) studies of the matrix of the bivalve Atrina embedded in vitrified ice show that the interlamellar sheets are composed mainly of highly ordered and aligned β-chitin fibrils. The silk, which is quantitatively an important component of the matrix, could not be imaged within the sheets. Organic material was, however, observed between sheets. We infer that this is the location of the silk. As this material reveals no regular structure, we suggest that at least prior to mineralization the silk is in the form of a hydrated gel. This is supported by cryo-TEM structural observations of an artificial assembly of β-chitin with and without silk. This view of the nacreous organic matrix significantly changes previous models of the matrix structure and hence hypotheses pertaining to the mechanisms by which mineral formation occurs.

Original languageAmerican English
Pages (from-to)8-17
Number of pages10
JournalJournal of Structural Biology
Volume135
Issue number1
DOIs
StatePublished - 2001
Externally publishedYes

Bibliographical note

Funding Information:
We thank Talmon Arad for his help in the electron microscopy work, Ilana Sabanay for her assistance with the cryomicrotomy, and Dr. Linda Shimon for helping with the X-ray diffraction. We are grateful to Professor Wolfie Traub for his advice. S.W. is the incumbent of the I. W. Abel Professorial Chair of Structural Biology, and L.A. is the incumbent of the Dorothy and Patrick Gorman Professorial Chair. This work was supported by a United States–Israel Binational Foundation grant and by the Minerva Foundation.

Keywords

  • Biomineralization
  • Chitin
  • Cryo-TEM
  • Mollusk
  • Silk
  • Vitrified sections

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