The molecular structure of green fluorescent protein

The crystal structure of recombinant wild-type green fluorescent protein (GFP) has been solved to a resolution of 1.9 Å by multiwavelength anomalous dispersion phasing methods. The protein is in the shape of a cylinder, comprising 11 strands of ß-sheet with an α-helix inside and short helical segments on the ends of the cylinder. This motif, with ß-structure on the outside and α-helix on the inside, represents a new protein fold, which we have named the ß-can. Two protomers pack closely together to form a dimer in the crystal. The fluorophores are protected inside the cylinders, and their structures are consistent with the formation of aromatic systems made up of Tyr86 with reduction of its Cα-Cß bond coupled with cyclization of the neighboring glycine and serine residues. The environment inside the cylinder explains the effects of many existing mutants of GFP and suggests specific side chains that could be modified to change the spectral properties of GFP. Furthermore, the identification of the dimer contacts may allow mutagenic control of the state of assembly of the protein.