Nature Struct. Biol. 9, 646–652 (2002).

The orientation of the molecule in Fig. 2a was inconsistent with the description in the legend. The correct figure is reproduced here. In addition, the reference at the end of the Fig. 2 legend was incorrect. The correct reference should be ref. 48. The correct sentence should read “(For more details, see http://mccammon.ucsd.edu/ and ref. 48)”. The authors apologize for any inconvenience this may have caused.