The green fluorescent-like protein family consists of fluorescent proteins and non-fluorescent chromoproteins, derived from several species of Cnidarians, as well as certain diazotrophic bacteria [11929996, 12502888]. These proteins range in their absorption wavelength maximum, and are often classified by their colour: green, yellow, red and purple-blue. These colour differences arise from changes in the structure of the chromophore, which is generated internally by auto-catalysis. The chromophore comprises Ser65-Tyr66-Gly67 in Aequorea victoria, which forms a five-member ring after its modification. In the bioluminescent organism A. victoria, GFP acts to transform the blue light emitted from aequorin into green light. However, most organisms with GFP-like molecules are not bioluminescent, and in some cases are not even fluorescent. These proteins all display a beta-can structure, which surrounds the chromophore and acts to shield it against quenching agents.
The G2 domain of nidogen contains a beta-can structure that exhibits extraordinary similarity to GFP, even though their sequences show only low sequence identity . Nidogen is a component of basement membranes, whose interactions with other basement membrane proteins contribute to the assembly and function of the basement membrane. The G2 domain serves as a protein-binding module. The structure is similar enough between GFP and the G2 domain of nidogen to suggest a common ancestral origin.
More information about this protein can be found at Protein of the Month: Green Fluorescent Protein.