Identification of the major proteins of the organic matrix of emu (Dromaius novaehollandiae) and rhea (Rhea americana) eggshell calcified layer

1. The eggshell is a composite consisting of 95% calcite and an organic matrix. 2. While many proteins of the chicken eggshell matrix have already been identified, little is known about the matrix of other birds. 3. Isolation of the emu and rhea eggshell matrix and analysis of its major constituents showed that the predominant components were C-type lectin-like proteins related to those of ostrich, chicken and goose. 4. Serum albumin, vitelline membrane outer layer protein I (VMO-I) and the turpentine-induced acute phase serum protein 18-B were identified as minor components of the emu shell matrix. Both eggshell matrices also contained a novel proline- and alanine-rich protein. 5. Like ostrich, and unlike chicken and goose, both emu and rhea eggshell matrix contained two different C-type lectin-like proteins as major components, indicating that the occurrence of two proteins of this family may be widespread among ratites.