Fluoroproline variants of EGFP.

<p>(A) Characteristic β-barrel structure of EGFP with the 10 Pro residues highlighted. Cro66 indicates the fluorophore. (B) Chemical structures of proline and the two proline analogs, (2<i>S</i>,4<i>S</i>)-4-fluoroproline ((4<i>S</i>)-FPro), and (2<i>S</i>,4<i>R</i>)-4-fluoroproline ((4<i>R</i>)-FPro). (C) Expression profile of EGFP and its 4-FPro variants in <i>E. coli</i>. EGFP and (4<i>S</i>)-FPro-EGFP are predominantly soluble, whereas (4<i>R</i>)-FPro-EGFP is insoluble. Purified EGFP was applied as the molecular weight marker (M) and is indicated by the arrow; S, soluble protein fraction; I, insoluble protein fraction. Proteins were separated by SDS-PAGE and stained with Coomassie Brillant Blue.