Acta Cryst. (2013). D69, 960-967 [ doi:10.1107/S0907444913003569 ]
Abstract: The -crystallin superfamily includes highly diverse proteins belonging to all of the kingdoms of life. Based on structural topology, these proteins are considered to be evolutionarily related to the long-lived -crystallins that constitute the vertebrate eye lens. This study reports the crystallographic structure at 0.99 Å resolution of the two-domain -crystallin (geodin) from the sponge Geodia cydonium. This is the most ancient member of the -crystallin superfamily in metazoans. The X-ray structure shows that the geodin domains adopt the typical -crystallin fold with a paired Greek-key motif, thus confirming the hypothesis that the crystallin-type scaffold used in the evolution of bacteria and moulds was recruited very early in metazoans. As a significant new structural feature, the sponge protein possesses a unique interdomain interface made up by pairing between the second motif of the first domain and the first motif of the second domain. The atomic resolution also allowed a detailed analysis of the calcium-binding site of the protein.
PDB reference: 4iau
Keywords: crystallins; atomic resolution; calcium binding; domain interactions; folding; Greek-key motif; Tyr corner; Trp corner.
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