She Sells Sea Shells--And Scientists Solve Their Secrets

When you pick up a sea shell on the seashore this summer, forget about its beauty for a moment and pay attention to its texture and strength. Scientists have long sought to explain how clams, snails and other mollusks control their shell-building process, arranging minerals in intricate patterns with remarkable precision.

Weizmann Institute researchers have now put a major piece of this puzzle in place. Their findings, described in a recent issue of Science, may one day lead to new ideas for designing improved composite materials, such as those used in aircraft and spaceship parts, orthopedic prostheses and a variety of other devices.

Mollusk shells are made of a natural composite material. They consist of a supporting protein framework filled with calcium carbonate crystals. These crystals come in two types, with one often forming the rougher outer layer of the shell, and the other--commonly known as mother-of-pearl--the shiny inner one. Their source material is the same, but minor structural differences grant them different properties and appearance. Growing the right kind of crystal in the right place is crucial for the strength of the shell, but how do the mollusks achieve this?

Prof. Lia Addadi, Prof. Stephen Weiner and Dr. Shira Albeck of the Institute's Structural Biology Department, together with Dr. Giuseppe Falini of the University of Bologna, have shown that the mollusks control the formation of the appropriate crystal type by manufacturing two different "support" proteins, each specializing in a different crystal type. These proteins then go on to regulate the entire process of determining which type of crystal goes where.

The scientists now intend to study the structure of these protein molecules, perhaps helping materials researchers to mimic the mollusks, amazing "engineering" talents.

Additional Information

Prof. Weiner holds the I.W. Abel Professorial Chair of Structural Biology, and Prof. Addadi, the Patrick Gorman Profes-sorial Chair of Biological Ultrastructure. Their study was supported by a U.S.-Israel Binational Science Foundation grant.