Glassin, a histidine-rich protein from the siliceous skeletal system of the marine sponge Euplectella, directs silica polycondensation

Hexactinellid sponges of the genus Euplectella produce highly ordered and mechanically robust skeletal systems of amorphous hydrated silica. The high damage tolerance of their constituent skeletal elements and the environmentally benign conditions under which these sponges form have prompted additional investigations into the characterization of the proteins driving the synthesis of these materials. In the present report, we describe a previously unidentified protein, named "glassin," extracted from the demineralized skeletal elements of Euplectella. Glassin is a histidine-, aspartic acid-, threonine-, and proline-rich protein and directs silica polycondensation at neutral pH and room temperature.