Expression, purification, crystallization and preliminary X-ray analysis of eCGP123, an extremely stable monomeric green fluorescent protein with reversible photoswitching properties.

Enhanced consensus green protein variant 123 (eCGP123) is an extremely thermostable green fluorescent protein (GFP) that exhibits useful negative reversible photoswitching properties. eCGP123 was derived by the application of both a consensus engineering approach and a recursive evolutionary process. Diffraction-quality crystals of recombinant eCGP123 were obtained by the hanging-drop vapour-diffusion method using PEG 3350 as the precipitant. The eCGP123 crystal diffracted X-rays to 2.10 Å resolution. The data were indexed in space group P1, with unit-cell parameters a = 74.63, b = 75.38, c = 84.51 Å, α = 90.96, β = 89.92, γ = 104.03°. The Matthews coefficient (V(M) = 2.26 Å(3) Da(-1)) and a solvent content of 46% indicated that the asymmetric unit contained eight eCGP123 molecules.