Figure 3. Structural and functional characterization of DUF families.

(A) Distribution of DUF structures with regard to structural similarity and homology to previously known structures. The main pie chart shows overall percentages of DUF families with new folds, new folds partially similar to previously known folds, putative analogs, putative homologs, and recognizable homologs. The inset pie charts show the percentage of DUF families with proposed hypothesis about function in each of these six categories. (B) Impact of solved structures on hypotheses about function proposed for DUF families. (C) Distribution of C_α RMSD versus number of equivalent residues in structural alignments between first structural representatives of DUF families and the closest previously solved structures of the same fold. Dark blue circles indicate pairs with detectable sequence homology (recognizable homologs). Pairs with marginal homology confirmed by the solved structure (putative homologs) are shown by bright blue circles. Pairs with unresolved homology are shown as green circles. As expected, structural alignments of pairs with detectable homology tend to be longer and C_α RMSD values tend to be lower. For illustration, we also show the same data for 20 partial similarities between new folds found in DUF structures and previously known folds (orange circles). We note that, by definition, the set of partial similarities is limited to pairs with more than 50 equivalent residues and C_α RMSD below 3 Å.