PROTEIN SUPERFAMILIES AND DOMAIN SUPERFOLDS

As the protein sequence and structure databases expand rapidly a bette r understanding of the relationships between proteins is required. A c lassification is considered that extends the sequence-based superfamil ies to include proteins with similar function and three-dimensional st ructures but no sequence similarity. So far there are only nine protei n folds known to recur in proteins having neither sequence nor functio nal similarity. These folds dominate the structure database, represent ing more than 30 per cent of all determined structures. This observati on has implications for protein-fold recognition.