Figure 4

Structural environments for protein positions that show discrepancy between observed residue frequencies and their structure-based predictions. A. Histogram of accessible surface areas (ASA) for D/E residues at the positions that show largest discrepancy (P < 10^-100), correspond to elevated frequencies of D/E among sequence homologs (effective frequencies more than 0.5), and do not contact with positively charged R, K or H residues. B. An example local structural distortion caused by contacts of buried acidic residues. A fragment of structure (PDB ID 1 rhs) with aspartate beta bulge is shown. Backbone is colored with blue, sidechains with red. Contact formed by aspartate D32 through the side chain oxygen is marked.