A plot of residue entropy against the optimal sequence for CASP target T0171. Here the relative entropy is plotted against the optimal sequence of query T0171. Relative entropy is calculated from the alignments from the final iteration of the PSI-BLAST search of the Combined-nr database. The optimal sequence is drawn from the PSI-BLAST profile of the same target. Notice that the entropy flattens out and that this region of low entropy and low conservation coincides with the long stretch of repeated tryptophans in the optimal sequence. Entropy is shown on log scale.