Fecha de publicación: 03/05/2018 Fuente: WIPO "apis cerana" The present invention relates to compositions comprising: a polypeptide, wherein at least a portion of the polypeptide has a coiled coil structure; and a chelate comprising a chelating agent and a metal ion; and wherein the chelate is bound to at least one amino acid of the polypeptide. In a preferred embodiment the polypeptide is a silk fibroin, wherein at least a portion of the silk fibroin has a coiled coil structure.