FIGURE 6.

The comparison of PcrA W461E and EccNarG (Protein Data Bank code 1Q16) in the substrate access tunnel. The overlay of residue W461E PcrA from six chains of PcrA in the asymmetric unit of PcrAB was shown to be highly flexible due to the lack of hydrogen binding with Ser⁵⁹⁴ and the loss of π-stacking with Tyr¹⁶⁵. The corresponding residue Glu⁵⁸¹ in EccNarG (magenta) was stabilized by residue Asp⁸⁰¹ via hydrogen bonding. The wild-type PcrAB is shown in dark gray color with Trp⁴⁶¹ stabilized by π-stacking with Tyr¹⁶⁵.