Figure 6.

The combinatorial use of protein architectures correlates with propensity for flexibility. The number of distinct folds, which tend to participate only in single-domain proteins (blue bars) and in multi-domain proteins (combinatorial folds, red bars), is displayed in the order of increased diversity of folds in genomes. The greater use of combinatorial than single-domain folds in Metazoa is consistent with their propensity for flexibility rather than robustness, in comparison with plants and fungi. Bacteria use combinatorial folds to a greater extent than Archaea. This is also consistent with our prediction that Bacteria is more flexible than Archaea. (A) Free-living organisms. (B) Obligate parasites. See Datasheet S4 in Supplementary Material for Methods.