Matrix Proteins and Mineralization: An Overview

There is a wealth of information on the mineral and matrix components in bones and teeth, in the exoskeletons of invertebrates, and in dystrophic calcific deposits. This information includes detailed characterization of their physical and chemical composition and details on the gene localization and regulation of gene expression for the major and minor protein constituents. The reason that mineral deposition occurs in some tissues and not in others remains unclear. In this review, studies in solution, cell culture studies, and investigations in mutant animals will be surveyed to indicate which matrix proteins may affect mineralization. Most of the molecules that appear to be involved in initiation and regulation of biological mineral formation are anionic; they have structural features that facilitate interaction with mineral, cells, and other matrix molecules, and they can have more than one function. Despite extensive data it is not yet clear which of these molecules is absolutely essential for physiologic calcification in each of the calcified tissues.