Figure 1

PSI-BLAST score of the most similar protein with the same enzyme function versus PSI-BLAST score of the most similar protein with different enzyme function at the 1^st (upper left chart), 2^nd (upper right chart), 3^rd (lower left chart), and 4^th EC level (lower right chart). Calculation was conducted for non-redundant set of 3,135 chain sequences (amino acid identity < 90%) of known structure and enzyme function. Each PSI-BLAST score was taken after the third iteration using 10,278 non-redundant sequence chains (including 3,135) from the Protein Data Bank to build a sequence profile. In each of the charts there are four clusters of points (A, B, C, and D) separated by the horizontal and vertical line. The A and C groups correspond to sequences that are not similar to any enzyme with a different EC number. Two other clusters (B and D) contain proteins from sequence superfamilies that have more than one function. Last two groups (E and F – not shown in the charts) include proteins of orphan function in this dataset. F group contains sequences which are significantly similar to other proteins, while E group corresponds to singleton sequences.