Towards interpretation of intermolecular paramagnetic relaxation enhancement outside the fast exchange limit

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• 作者：Alberto Ceccon ; G. Marius Clore ; Vitali Tugarinov
• 关键词：Paramagnetic relaxation enhancement ; Chemical exchange ; Ligand binding ; Liposomes ; Protein ; nanoparticle interactions
• 刊名：Journal of Biomolecular NMR
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：66
• 期：1
• 页码：1-7
• 全文大小：940 KB
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Biophysics and Biomedical Physics
  Polymer Sciences
  Biochemistry
  
• 出版者：Springer Netherlands
• ISSN：1573-5001
• 卷排序：66

文摘

In an exchanging system between major and minor species, the transverse paramagnetic relaxation enhancement rate observed on the resonances of the major species (Γ₂app) is dependent upon the exchange regime between the species. Quantitative analysis of PRE data in such systems typically assumes that the overall exchange rate k_ex between the species is fast on the PRE time scale (k_ex ≫ Γ₂). Recently, we have characterized the kinetics of binding of the model protein ubiquitin to large (LUV) and small (SUV) unilamellar lipid-based nanoparticles or liposomes (Ceccon A, Tugarinov V, Bax A, Clore GM (2016). J Am Chem Soc 138:5789–5792). Building upon these results and taking advantage of a strong paramagnetic agent with an isotropic g-tensor, Gd3+, we were able to measure intermolecular methyl carbon and proton PREs between paramagnetically-tagged liposomes and ubiquitin. In the limit of fast exchange (k_ex ≫ Γ₂) the ratio of the apparent proton to carbon methyl PREs, (1H_m–Γ₂app)/(13C_m–Γ₂app), is equal to the square of the ratio of the gyromagnetic ratios of the two nuclei, (γ_Η/γ_C)2. However, outside the fast exchange regime, under intermediate exchange conditions (e.g. when Γ₂ is comparable in magnitude to k_ex) the (1H_m–Γ₂app)/(13C_m–Γ₂app) ratio provides a reliable measure of the ‘true’ methyl PREs.