RING fingers and B-boxes: zinc-binding protein-protein interaction domains.

The cysteine-rich zinc-binding motifs known as the RING and B-box are found in several unrelated proteins. Structural, biochemical, and biological studies of these motifs reveal that they mediate protein-protein interactions. Several RING-containing proteins are oncoproteins and recent data indicate that proapoptotic activities can be mediated through the RING. 1H NMR methods were used to determine the structures of RINGs and a B-box domain and to monitor the conformational changes these motifs undergo upon zinc ligation. This review discusses in detail the structural features of the RING and B-box domains. Further, possible structure function relationships for these motifs particularly in their role as protein interaction domains are discussed.