Lysine methylation: A strategy to improve in-cell NMR spectroscopy of proteins.

BACKGROUND: In-cell NMR is a valuable technique for investigating protein structure and function in cellular environments. However, challenges arise due to highly crowded cellular environment, where nonspecific interactions between the target protein and other cellular components can lead to signals broadening or disappearance in NMR spectra. RESULTS: We implemented chemical reduction methylation to selectively modify lysine residues on protein surfaces aiming to weaken charge interactions and recover obscured NMR signals. This method was tested on six proteins varying in molecular size and lysine content. While methylation did not disrupt the protein's native conformation, it successful restored some previously obscured in-cell NMR signals, particularly for proteins with high isoelectric points that decreased post-methylation. SIGNIFICANCE: This study affirms lysine methylation as a feasible approach to enhance the sensitivity of in-cell NMR spectra for protein studies. By mitigating signal loss due to nonspecific interactions, this method expands the utility of in-cell NMR for investigating proteins in their natural cellular environment, potentially leading to more accurate structural and functional insights.

Rapid Targeted Screening and Identification of Active Ingredients in Herbal Extracts through Ligand-Detected NMR and Database Matching.

Herbal extracts are rich sources of active compounds that can be used for drug screening due to their diverse and unique chemical structures. However, traditional methods for screening these compounds are notably laborious and time-consuming. In this manuscript, we introduce a new high-throughput approach that combines nuclear magnetic resonance (NMR) spectroscopy with a tailored database and algorithm to rapidly identify bioactive components in herbal extracts. This method distinguishes characteristic signals and structural motifs of active constituents in the raw extracts through a relaxation-weighted technique, particularly utilizing the perfect echo Carr-Purcell-Meiboom-Gill (peCPMG) sequence, complemented by precise 2D spectroscopic strategies. The cornerstone of our approach is a customized database designed to filter potential compounds based on defined parameters, such as the presence of CHn segments and unique chemical shifts, thereby expediting the identification of promising compounds. This innovative technique was applied to identifying substances interacting with choline kinase α (ChoKα1), resulting in the discovery of four new inhibitors. Our findings demonstrate a powerful tool for unraveling the complex chemical landscape of herbal extracts, considerably facilitating the search for new pharmaceutical candidates. This approach offers an efficient alternative to traditional methods in the quest for drug discovery from natural sources.

Real-Time Observation of Conformational Changes and Translocation of Endogenous Cytochrome c within Intact Mitochondria.

Cytochrome c (cyt c) is a multifunctional protein with varying conformations. However, the conformation of cyt c in its native environment, mitochondria, is still unclear. Here, we applied NMR spectroscopy to investigate the conformation and location of endogenous cyt c within intact mitochondria at natural isotopic abundance, mainly using widespread methyl groups as probes. By monitoring time-dependent chemical shift perturbations, we observed that most cyt c is located in the inner mitochondrial membrane and partially unfolded, which is distinct from its native conformation in solution. When suffering oxidative stress, cyt c underwent oxidative modifications due to increasing reactive oxygen species (ROS), weakening electrostatic interactions with the membrane, and gradually translocating into the inner membrane spaces of mitochondria. Meanwhile, the lethality of oxidatively modified cyt c to cells was reduced compared with normal cyt c. Our findings significantly improve the understanding of the molecular mechanisms underlying the regulation of ROS by cyt c in mitochondria. Moreover, it highlights the potential of NMR to monitor high-concentration molecules at a natural isotopic abundance within intact cells or organelles.

Real-Time NMR-Based Drug Discovery to Identify Inhibitors against Fatty Acid Synthesis in Living Cancer Cells.

Abnormal fatty acid metabolism is recognized as a key driver of tumor development and progression. Although numerous inhibitors have been developed to target this pathway, finding drugs with high specificity that do not disrupt normal cellular metabolism remains a formidable challenge. In this paper, we introduced a novel real-time NMR-based drug screening technique that operates within living cells. This technique provides a direct way to putatively identify molecular targets involved in specific metabolic processes, making it a powerful tool for cell-based drug screening. Using 2-13C acetate as a tracer, combined with 3D cell clusters and a bioreactor system, our approach enables real-time detection of inhibitors that target fatty acid metabolism within living cells. As a result, we successfully demonstrated the initial application of this method in the discovery of traditional Chinese medicines that specifically target fatty acid metabolism. Elucidating the mechanisms behind herbal medicines remains challenging due to the complex nature of their compounds and the presence of multiple targets. Remarkably, our findings demonstrate the significant inhibitory effect of P. cocos on fatty acid synthesis within cells, illustrating the potential of this approach in analyzing fatty acid metabolism events and identifying drug candidates that selectively inhibit fatty acid synthesis at the cellular level. Moreover, this systematic approach represents a valuable strategy for discovering the intricate effects of herbal medicine.

NMR Reveals the Conformational Changes of Cytochrome C upon Interaction with Cardiolipin.

Conformational change of cytochrome c (cyt c) caused by interaction with cardiolipin (CL) is an important step during apoptosis, but the underlying mechanism is controversial. To comprehensively clarify the structural transformations of cyt c upon interaction with CL and avoid the unpredictable alias that might come from protein labeling or mutations, the conformation of purified yeast iso-1 cyt c with natural isotopic abundance in different contents of CL was measured by using NMR spectroscopy, in which the trimethylated group of the protein was used as a natural probe. The data demonstrate that cyt c has two partially unfolded conformations when interacted with CL: one with Fe-His33 coordination and the other with a penta-coordination heme. The Fe-His33 coordination conformation can be converted into a penta-coordination heme conformation in high content of CL. The structure of cyt c becomes partially unfolded with more exposed heme upon interaction with CL, suggesting that cyt c prefers a high peroxidase activity state in the mitochondria, which, in turn, makes CL easy to be oxidized, and causes the release of cyt c into the cytoplasm as a trigger in apoptosis.

Structural basis of DNA binding to human YB-1 cold shock domain regulated by phosphorylation.

Human Y-box binding protein 1 (YB-1) is a multifunctional protein and overexpressed in many types of cancer. It specifically recognizes DNA/RNA through a cold shock domain (CSD) and regulates nucleic acid metabolism. The C-terminal extension of CSD and the phosphorylation of S102 are indispensable for YB-1 function. Until now, the roles of the C-terminal extension and phosphorylation in gene transcription and translation are still largely unknown. Here, we solved the structure of human YB-1 CSD with a C-terminal extension sequence (CSDex). The structure reveals that the extension interacts with several residues in the conventional CSD and adopts a rigid structure instead of being disordered. Either deletion of this extension or phosphorylation of S102 destabilizes the protein and results in partial unfolding. Structural characterization of CSDex in complex with a ssDNA heptamer shows that all the seven nucleotides are involved in DNA-protein interactions and the C-terminal extension provides a unique DNA binding site. Our DNA-binding study indicates that CSDex can recognize more DNA sequences than previously thought and the phosphorylation reduces its binding to ssDNA dramatically. Our results suggest that gene transcription and translation can be regulated by changing the affinity of CSDex binding to DNA and RNA through phosphorylation, respectively.

Monitoring alkaline transitions of yeast iso-1 cytochrome c at natural isotopic abundance using trimethyllysine as a native NMR probe.

Spectral overlap makes it difficult to use NMR for mapping the conformational profile of heterogeneous conformational ensembles of macromolecules. Here, we apply a 1H-14N HSQC experiment to monitor the alkaline conformational transitions of yeast iso-1 cytochrome c (ycyt c) at natural isotopic abundance. Trimethylated Lys72 of ycyt c is selectively detected by a 1H-14N HSQC experiment, and used as a probe to trace conformational transitions of ycyt c under alkaline conditions. It was found that at least four different conformers of ycyt c coexisted under alkaline conditions. Besides the native structure, Lys73 or Lys79 coordinated conformers and a partially unfolded state with exposed heme were observed. These results indicate that the method is powerful at simplifying spectra of a trimethylated protein, which makes it possible to study complex conformational transitions of naturally extracted or chemically modified trimethylated protein at natural isotopic abundance.

Synthesis, in silico and in vivo blood brain barrier permeability of ginkgolide B cinnamate.

Ginkgolide B, one of the important components of Ginkgo biloba extracts, has been revealed to exhibit great potential in therapy of cerebrovascular diseases. However the lack of permeability greatly limited it from further clinical application. Based on the prediction model for blood brain barrier (BBB) permeation, herein a potential brain-targeting analog ginkgolide B cinnamate (GBC) was successfully synthesized and characterized. After intravenous administration of GBC or GB, liquid chromatography tandem mass spectrometry (LC-MS/MS) was conducted to determine the analog in rat plasma and brain. The results showed that GBC had a significant increase in BBB permeability. A significant 1.61-times increase in half-life was observed for GBC and the drug targeting index (DTI) value was calculated to be 9.91. The experiment results matched well with the predicted one, which revealed that BBB permeability prediction model combined with in vivo study could be used as a quick, feasible and efficient tool for brain-targeting drug design.