ASGSB 1998 Annual Meeting Abstracts

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AN OVERVIEW OF VERTEBRATE MINERALIZATION WITH EMPHASIS ON COLLAGEN-MINERAL INTERACTION. W.J. Landis. Department of Orthopedic Surgery, Children’s Hospital and Harvard Medical School, Boston, MA 02115

This presentation summarizes current understanding of molecular and macromolecular relationships between collagen and mineral and their importance in the progressive growth and development of normally calcifying bone, cartilage, tendon, dentin, and cementum among vertebrate tissues. Collagen represents the principal organic component in such tissues and it strictly mediates the nucleation, growth, and development of the mineral, a calcium phosphate salt (apatite). The mineral of collagenous tissues is composed of crystals having unusually small sizes (minimally ~45 x 30 x 2-4 nm) and shapes resembling irregular platelets. The crystallographic c-axes follow the longest dimension of the crystals, corresponding to their [100] faces, and, in association with collagen, the c-axes are aligned in parallel to the collagen long axes. The [100] faces of the crystals also lie generally parallel (± 20) to each other. Thus, the size, shape, alignment, and orientation of the crystals in vertebrate tissues are highly regulated. Crystal location and distribution are also ordered. Control of all such parameters of mineral formation is a consequence of collagen assembly and aggregation at different levels of structural hierarchy. Fundamentally, the hole and overlap zones (A.J. Hodge and J.A. Petruska, in G.N. Ramachandran [Ed.], Aspects of Protein Structure, Academic Press, NY, pp.289-300, 1963) of adjacent collagen molecules appear in very close register. This arrangement in three dimensions would create spatial gaps in the form of channels through collagen molecular assemblages. The channels likely define specific stereochemical and electrostatic charge characteristics that in turn support sites for crystal nucleation and accommodate apatite growth with the crystal character described above. The interaction between collagen and mineral in this manner leads to a composite tissue having improved strength and biomechanical properties different from those of either component separately considered. Conversely, changes in collagen content, assembly, or aggregation could have profound effects on mineralization and subsequently on the nature of tissue integrity and mechanical behavior.

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