The molecule illustrated on the cover is the tryptophanyl glutamic acid (Trp-Glu) dipeptide in the 1+ charge state, presented by Azaria Eisenberg and Laura Juszczak on page 1549. It represents a single conformation from a 30 ns molecular dynamics simulation. Three discrete values of the Chi 1 dihedral angle describe the motion of all Trp-Glu charge states: 60°, 180°, and 300°. For the Chi 1 angle of 60° shown here, the backbone curls over the indole ring, resulting in numerous backbone–ring noncovalent interactions. An electrostatic potential surface cuts through the indole plane, revealing the uneven charge distribution over the indole ring (red, −0.232 atomic units; blue, 0.207 atomic units).