SM50 repeat-polypeptides self-assemble into discrete matrix subunits and promote appositional calcium carbonate crystal growth during sea urchin tooth biomineralization.

The two major proteins involved in vertebrate enamel formation and echinoderm sea urchin tooth biomineralization, amelogenin and SM50, are both characterized by elongated polyproline repeat domains in the center of the macromolecule. To determine the role of polyproline repeat polypeptides in basal deuterostome biomineralization, we have mapped the localization of SM50 as it relates to crystal growth, conducted self-assembly studies of SM50 repeat polypeptides, and examined their effect on calcium carbonate and apatite crystal growth. Electron micrographs of the growth zone of Strongylocentrotus purpuratus sea urchin teeth documented a series of successive events from intravesicular mineral nucleation to mineral deposition at the interface between tooth surface and odontoblast syncytium.

Membranes, minerals, and proteins of developing vertebrate enamel.

Developing tooth enamel is formed as organized mineral in a specialized protein matrix. In order to analyze patterns of enamel mineralization and enamel protein expression in species representative of the main extant vertebrate lineages, we investigated developing teeth in a chondrichthyan, the horn shark, a teleost, the guppy, a urodele amphibian, the Mexican axolotl, an anuran amphibian, the leopard frog, two lepidosauria, a gecko and an iguana, and two mammals, a marsupial, the South American short-tailed gray opossum, and the house mouse. Electron microscopic analysis documented the presence of a distinct basal lamina in all species investigated.

Conservation and variation in enamel protein distribution during vertebrate tooth development.

Vertebrate enamel formation is a unique synthesis of the function of highly specialized enamel proteins and their effect on the growth and organization of apatite crystals. Among tetrapods, the physical structure of enamel is highly conserved, while there is a greater variety of enameloid tooth coverings in fish. In the present study, we postulated that in enamel microstructures of similar organization, the principle components of the enamel protein matrix would have to be highly conserved.