Journal:JBIC:9

<applet load="Jbic91a.pdb" size="600" color="" frame="true" spin="on" Scene ="Journal:JBIC:9/Cv/3" align="right" caption=""/>

<big>Jens Loebus, Estevão A. Peroza, Nancy Blüthgen, Thomas Fox, Wolfram Meyer Klaucke, Oliver Zerbe and Eva Freisinger</big><ref>doi</ref>

Ec-1 (Early Cys-labelled protein) from ''Triticum aestivum'' (common bread wheat) belongs to the family of plant metallothioneins. Metallothioneins in general are small (up to approx. 8 kDa) Cys-rich proteins with the ability to coordinate d10 transition metal ions with high thermodynamic affinity. <scene name='Journal:JBIC:9/Cv/9'>Thereby metal-thiolate cluster structures are formed.</scene> The function of these protein is presumably to be found in metal ion homeostasis (Zn(II), Cu(I)), detoxification (Cd(II), Hg(II), etc.), and possibly also in reactive oxygen species scavenging. Wheat Ec-1 consists of 81 amino acids and forms two distinctive domains. The NMR structure of the larger C-terminal β(E)-domain has been already described (PDB ID [[2kak]], <ref name="Peroza">PMID:19361445</ref>) and accommodates four Zn(II) ions. The NMR solution structure of the smaller N-terminal γ-domain shown here consists of the first 24 amino acids of the protein (plus two additional N-terminal vector-derived amino acid residues). The six Cys residues of the γ-domain form a cluster with two Zn(II) or Cd(II) ions similar to the one found in the yeast transcription factor GAL4 (PDB ID [[1aw6]],<ref name="Baleja">PMID:9460244</ref>). The resulting NMR γ-Ec-1 structures containing the metal cluster arrangements <scene name='Journal:JBIC:9/Cv/10'>Cys-9/21</scene> or <scene name='Journal:JBIC:9/Cv/11'>Cys-9/3</scene> were obtained. <scene name='Journal:JBIC:9/Cv/6'>A superposition of the backbone atoms of conformers</scene>, in which either Cys-3 or Cys-21 were constrained to be the bridging ligands, revealed that only small structural adaptations were necessary to transform one form into the other. In the case with Cys-9/21 connectivity <scene name='Journal:JBIC:9/Cv/12'>Cys21</scene> forms bridge between two Zn(II) atoms (in addition to Cys9), whereas in the case with Cys-9/3 arrangement <scene name='Journal:JBIC:9/Cv/8'>Cys3</scene> participate in the bridge formation. This two-metal ion cluster, as well as the metal ion arrangement found in the larger β(E)-domain, represent new coordination modes that were unprecedented for the superfamily of metallothioneins so far. The functional significance of these findings has to be awaited.