Protein environment affects the water–tryptophan binding mode. MD, QM/MM, and NMR studies of engrailed homeodomain mutants

Water molecules can interact with the π-face of tryptophan either forming an O–H⋯π hydrogen bond or by a lone-pair⋯π interaction. Surrounding amino acids can favor the one or the other interaction type.

Photo-control of DNA binding by an engrailed homeodomain–photoactive yellow protein hybrid

A photo-controlled version of the engrailed homeodomain (zENG) was created by inserting the homeodomain into a surface loop of a circularly permuted version of the photoactive yellow protein (cPYP).