The mechanism of folding robustness revealed by the crystal structure of extra-superfolder GFP.

Stability of green fluorescent protein (GFP) is sometimes important for a proper practical application of this protein. Random mutagenesis and targeted mutagenesis have been used to create better-folded variants of GFP, including recently reported extra-superfolder GFP. Our aim was to determine the crystal structure of extra-superfolder GFP, which is more robustly folded and stable than GFP and superfolder GFP. The structural and structure-based mutagenesis analyses revealed that some of the mutations that created extra-superfolder GFP (F46L, E126K, N149K, and S208L) contribute to folding robustness by stabilizing extra-superfolder GFP with various noncovalent bonds.