Rational Design of Protein Stability: Effect of (2S,4R)-4-Fluoroproline on the Stability and Folding Pathway of Ubiquitin

BACKGROUND: Many strategies have been employed to increase the conformational stability of proteins. The use of 4-substituted proline analogs capable to induce pre-organization in target proteins is an attractive tool to deliver an additional conformational stability without perturbing the overall protein structure. Both, peptides and proteins containing 4-fluorinated proline derivatives can be stabilized by forcing the pyrrolidine ring in its favored puckering conformation. The fluorinated pyrrolidine rings of proline can preferably stabilize either a C(γ)-exo or a C(γ)-endo ring pucker in dependence of proline chirality (4R/4S) in a complex protein structure. To examine whether this rational strategy can be generally used for protein stabilization, we have chosen human ubiquitin as a model protein which contains three proline residues displaying C(γ)-exo puckering. METHODOLOGY/PRINCIPAL FINDINGS: While (2S,4R)-4-fluoroproline ((4R)-FPro) containing ubiquitinin can be expressed in related auxotrophic Escherichia coli strain, all attempts to incorporate (2S,4S)-4-fluoroproline ((4S)-FPro) failed. Our results indicate that (4R)-FPro is favoring the C(γ)-exo conformation present in the wild type structure and stabilizes the protein structure due to a pre-organization effect. This was confirmed by thermal and guanidinium chloride-induced denaturation profile analyses, where we observed an increase in stability of -4.71 kJ·mol(-1) in the case of (4R)-FPro containing ubiquitin ((4R)-FPro-ub) compared to wild type ubiquitin (wt-ub). Expectedly, activity assays revealed that (4R)-FPro-ub retained the full biological activity compared to wt-ub. CONCLUSIONS/SIGNIFICANCE: The results fully confirm the general applicability of incorporating fluoroproline derivatives for improving protein stability. In general, a rational design strategy that enforces the natural occurring proline puckering conformation can be used to stabilize the desired target protein

Recommendations for performing, interpreting and reporting hydrogen deuterium exchange mass spectrometry (HDX-MS) experiments.

Hydrogen deuterium exchange mass spectrometry (HDX-MS) is a powerful biophysical technique being increasingly applied to a wide variety of problems. As the HDX-MS community continues to grow, adoption of best practices in data collection, analysis, presentation and interpretation will greatly enhance the accessibility of this technique to nonspecialists. Here we provide recommendations arising from community discussions emerging out of the first International Conference on Hydrogen-Exchange Mass Spectrometry (IC-HDX; 2017). It is meant to represent both a consensus viewpoint and an opportunity to stimulate further additions and refinements as the field advances

Native Page analysis of M and Z α₁AT under HDX conditions.

<p>M and Z α₁AT were incubated in D₂O buffered with 10 mM Tris (pD 8) at 25°C for up to 2500 seconds. Samples of the proteins were then analyzed by 10% Native PAGE. (A): M α₁AT t = 0 seconds; (B) M α₁AT t = 2500 seconds; (C) Z α₁AT t = 0 seconds; (D) Z α₁AT t = 2500 seconds and (E) Z α₁AT polymers purified directly from <i>P. Pastoris</i> 10].</p

Details of the peptides derived from pepsin digestion and tandem mass spectrometry experiments.

<p>The relative masses used in this study were determined using Sequest.</p><p>Details of the peptides derived from pepsin digestion and tandem mass spectrometry experiments.</p

Differences in hydrogen exchange at 2000 seconds between M and Z α₁AT.

<p>The amino acid sequence of α₁AT is shown with secondary structure highlighted above the sequence. The 18 peptides used in the study are noted, as double headed arrows. The peptides for both M and Z α₁AT are colored according to the percentage deuterium incorporation at 2000 seconds: class 1 80–100% (red), class 2 30–80% (yellow) and class 3 0–30% (blue).</p