Fluorescein: A Photo-CIDNP Sensitizer Enabling Hypersensitive NMR Data Collection in Liquids at Low Micromolar Concentration

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is a powerful approach for sensitivity enhancement in NMR spectroscopy. In liquids, intermolecular photo-CIDNP depends on the transient bimolecular reaction between photoexcited dye and sample of interest. Hence the extent of polarization is sample-concentration dependent. This study introduces fluorescein (FL) as a photo-CIDNP dye whose performance is exquisitely tailored to data collection at extremely low sample concentrations. The photo-CIDNP resonance intensities of tryptophan in the presence of either FL or FMN (i.e., the routinely employed flavin mononucleotide photosensitizer) in the liquid state show that FL yields superior sensitivity and enables rapid data collection down to an unprecedented 1 μM concentration. This result was achieved on a conventional spectrometer operating at 14.1 T and equipped with a room-temperature probe (i.e., noncryogenic). Kinetic simulations show that the excellent behavior of FL arises from its long excited-state triplet lifetime and superior photostability relative to conventional photo-CIDNP sensitizers

A “Steady-State” Relaxation Dispersion Nuclear Magnetic Resonance Experiment for Studies of Chemical Exchange in Degenerate ¹H Transitions of Methyl Groups

Degenerate spin-systems consisting of magnetically equivalent nuclear spins, such as a 1H3 spin-system in selectively 13CH3-labeled proteins, present considerable challenges for the design of Carr–Purcell–Meiboom–Gill (CPMG) relaxation dispersion NMR experiments to characterize chemical exchange on the micro-to-millisecond time-scale. Several approaches have been previously proposed for the elimination of deleterious artifacts observed in methyl 1H CPMG relaxation dispersion profiles obtained for (13C)1H3 groups. We describe an alternative, experimentally simple solution and design a “steady-state” methyl 1H CPMG scheme, where 90° or acute-angle (1H radiofrequency pulses are applied after each CPMG echo in-phase with methyl 1H magnetization, resulting in the establishment of a “steady-state” for effective rates of magnetization decay. A simple computational procedure for quantitative analysis of the “steady-state” CPMG relaxation dispersion profiles is developed. The “steady-state” CPMG methodology is applied to two protein systems where exchange between major and minor species occurs in different regimes on the chemical shift time-scale

Kinetic Trapping of Folded Proteins Relative to Aggregates under Physiologically Relevant Conditions

Anfinsen’s thermodynamic hypothesis does not explicitly take into account the possibility of protein aggregation. Here, we introduce a cyclic-perturbation approach to prove that not only the native state but also soluble aggregates of most proteins can be highly populated under mild, physiologically relevant conditions, even at very low concentration. Surprisingly, these aggregates are not necessarily amyloid in nature and are usually not observed in bioactive proteins due to the extremely low kinetic flux from the native state toward a region of the chemical-potential landscape encoding aggregates. We first illustrate this concept for the representative model protein apomyoglobinat room temperature and no denaturantand demonstrate kinetic trapping of the native state relative to at least two different types of soluble, predominantly nonamyloid aggregates. The concentration and temperature dependence of aggregation confirm the above scenario. Extension of our analysis to the Escherichia coli proteome shows that the majority of the soluble bacterial proteome is also kinetically trapped in the nonaggregated state. Hence, the existence and low kinetic accessibility of large aggregates at room temperature and pH 6–7 is a general phenomenon. We also show that the average critical protein concentration for aggregation of most of the bacterial proteome is extremely small, much lower than the typical cellular protein concentration. Hence, the thermodynamic driving force for protein aggregation is large even if aggregation does not usually occur in healthy cells due to kinetic trapping. A broader view of Anfinsen’s thermodynamic hypothesis encompassing all protein states, including aggregates, is necessary to understand the behavior of proteins in their natural environment

Profile of genetic mutations and aberrant methylation.

<p>(A) Mutation status of RAS pathway genes and secondary genes (<i>SETBP1</i> and <i>JAK3</i>) identified as gene targets. Aberrant methylation scores (AMS) in a cohort of 92 patients with juvenile myelomonocytic leukemia are summarized. A rhombus denotes a patient with Noonan syndrome-associated myeloproliferative disorder. (B) Mutations in <i>SETBP1</i> and <i>JAK3</i> were associated with a higher AMS. The mean AMS of patients with <i>SETBP1</i> and/or <i>JAK3</i> mutations was higher than that of patients without secondary mutations (p = 0.03).</p

Summary of DNA methylation in candidate genes.

<p>(A) The dot plot represents the frequencies of methylated CpG sites for each candidate gene in the 92 patients with juvenile myelomonocytic leukemia. Aberrant hypermethylation was defined as >3 standard deviations above the mean methylation level of the healthy control population. The threshold values of each gene are shown as red broken lines. (B) Kaplan–Meier plots of the patient groups, defined by aberrant methylation of the indicated genes, are shown for <i>BMP4</i>, <i>CALCA</i>, <i>CDKN2A</i>, <i>CDKN2B</i>, <i>H19</i>, and <i>RARB</i>.</p

Hypermethylation status and clinical outcome in patients with juvenile myelomonocytic leukemia (JMML).

<p>(A) Kaplan–Meier curves represent the probability of transplantation-free survival (TFS) in the 92 patients with JMML. TFS was defined as the probability of being alive and transplantation free. Both death and transplantation were considered events. The probability of 5-year TFS in the aberrant methylation score (AMS) 0 cohort (solid line) was significantly higher than that in the AMS 1–2 (long dashed line) and AMS 3–4 cohorts (dashed line), p < 0.001. (B) Kaplan–Meier curves represent the probability of overall survival (OS) in the 92 patients with JMML. Death was considered an event. The probability of OS in both the AMS 0 (solid line) and 1–2 cohorts (long dashed line) was significantly higher than that in the AMS 3–4 cohort (dashed line), p < 0.001.</p

Patient characteristics.

<p>Patient characteristics.</p

Multivariate model for transplantation-free and overall survival.

<p>Multivariate model for transplantation-free and overall survival.</p