(4R)- and (4S)-fluoroproline in the conserved cis-prolyl peptide bond of the thioredoxin fold: tertiary structure context dictates ring puckering.

Fine-tuning protein stability: The non-natural amino acids (2S,4R)- and (2S,4S)-fluoroproline modulate protein stability by biasing the proline ring pucker and the cis/trans equilibrium of prolyl peptide bonds. We incorporated both fluoroproline stereoisomers at the invariant cis-proline residue of the thioredoxin fold. The results show that tertiary structure context overrules the conformational preferences of fluoroprolines.