Synthetic Biology of Proteins: Tuning GFPs Folding and Stability with Fluoroproline
Figure 4
X-ray structure of the proline-rich pentapeptide (4S)-FPro54-Val55-(4S)-FPro56-Trp57-(4S)-FPro58 (PVPWP).
The continuous electron density (grey, 2Fo-Fc; contouring levels 1 σ) indicates fluorine atoms at the 4S-position in three buried Pro residues (54, 56, 58). Their experimental electron densities are localized unambiguously (image preparation with PYMOL (http://pymol.sourceforge.net/)). Out of the three Pro residues forming trans peptide bonds, only Pro56 exhibits predominant Cγ-exo pucker whereas the other two have pyrrolidine rings with Cγ-endo conformation. The rigid local secondary structure of this motif forces the (4S)-fluorinated pyrrolidine ring of (4S)-FPro56 into a stereochemically unfavorable Cγ-exo pucker.