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The aggregation of amyloidogenic proteins is often related to the occurrence of neurodegenerative diseases, including fused in sarcoma protein (FUS) in frontotemporal lobar degeneration and amyotrophic lateral sclerosis diseases. Recently, the SERF protein family has been reported to have a significant regulatory effect on amyloid formation, but it is still unclear about the detailed mechanisms of SERF acting on different amyloidogenic proteins. Herein, nuclear magnetic resonance (NMR) spectroscopy and fluorescence spectroscopy were used to explore interactions of ScSERF with three amyloidogenic proteins FUS‐LC, FUS‐Core, and α‐Synuclein. NMR chemical shift perturbations reveal them sharing similar interaction sites on the N‐terminal region of ScSERF. However, the amyloid formation of α‐Synuclein protein is accelerated by ScSERF, while ScSERF inhibits fibrosis of FUS‐Core and FUS‐LC proteins. Both the primary nucleation and the total amount of fibrils produced are detained. Our results suggest a diverse role of ScSERF in regulating the fibril growth of amyloidogenic proteins. [ABSTRACT FROM AUTHOR]

Nanobodies (Nbs) are the variable domain of the heavy-chain antibodies produced from Camelidae, which possess comparable binding affinities and specificity to conventional antibodies. Nbs have become valuable and versatile tools for numerous biotechnology applications due to their small size (12–15 kDa), high solubility, exceptional stability, and facile genetic manipulation. The interactions between Nbs and protein antigens have been well-studied, but less work has been done to characterize their ability to bind small molecule haptens. Here we present the backbone and side-chain assignments of the 1H, 13C and 15N resonances of Nb26 (123 amino acids), a nanobody that recognizes the hapten aflatoxin B1 (AFB1). These assignments are preliminary work towards the determination of the structure of free Nb26 using NMR spectroscopy, which will provide useful information about the complex structure of "Nb26-AFB1" and the recognition mechanism about how Nb26 binds to AFB1. [ABSTRACT FROM AUTHOR]

Macromolecular crowding and confinement are two factors that potentially affect protein structure and function in a complex cellular environment. The confinement effect on the structure and function of holoCaM [Ca2+-loaded calmodulin (CaM)], a two-domain protein involved in many calcium-mediated signaling pathways, has been investigated previously. However, little is known about how macromolecular crowding affects holoCaM structure and function. Here, the structure-function correlations of holoCaM are investigated in macromolecular crowded environments. It was found that macromolecular crowding impacts its structure and function mildly. The major conformational states are still extended conformation with inter-domain separation in crowded environment as well as those in dilute solution, but the population of transiently compact conformation increases compared to dilute solution. Furthermore, macromolecular crowding facilitates the binding of CaM with AcN19 peptide (CaM-bind domain of α- syn). This study provides a direct comparison for macromolecular crowding and confinement effects on protein structure and function, which helps to understand chemistry regulation in living cells. [ABSTRACT FROM AUTHOR]

Many cellular reactions involving proteins, including their biosynthesis, misfolding, and transport, occur in confined compartments. Despite its importance, a structural basis of understanding of how confined environments alter protein function is still lacking. Herein, we explore structure-function correlations of calmodulin (CaM), a multidomain protein involved in many calcium-mediated signaling pathways, in reverse micelles. Confinement dramatically alters CaM structure and function. The protein forms an extended structure in bulk water, but becomes compacted in reverse micelles. In addition, confinement changes the function of CaM. Specifically, the protein binds the MLCK, AcN19, and somatostatin peptides in dilute buffer, but binds only the MLCK and AcN19 peptides in reverse micelles. In summary, we determined a new CaM structure in reverse micelles and demonstrate that confinement can modulate both protein structure and function. [ABSTRACT FROM AUTHOR]

The glutamine binding protein (GlnBP) binds l-glutamine and cooperates with its cognate transporters during glutamine uptake. Crystal structure analysis has revealed an open and a closed conformation for apo- and holo-GlnBP, respectively. However, the detailed conformational dynamics have remained unclear. Herein, we combined NMR spectroscopy, MD simulations, and single-molecule FRET techniques to decipher the conformational dynamics of apo-GlnBP. The NMR residual dipolar couplings of apo-GlnBP were in good agreement with a MD-derived structure ensemble consisting of four metastable states. The open and closed conformations are the two major states. This four-state model was further validated by smFRET experiments and suggests the conformational selection mechanism in ligand recognition of GlnBP. [ABSTRACT FROM AUTHOR]

We used Xenopus laevis oocytes, a paradigm for a variety of biological studies, as a eukaryotic model system for in-cell protein NMR spectroscopy. The small globular protein GB1 was one of the first studied in Xenopus oocytes, but there have been few reports since then of high-resolution spectra in oocytes. The scarcity of data is at least partly due to the lack of good labeling strategies and the paucity of information on resonance broadening mechanisms. Here, we systematically evaluate isotope enrichment and labeling methods in oocytes injected with five different proteins with molecular masses of 6 to 54 kDa. 19F labeling is more promising than 15N, 13C, and 2H enrichment. We also used 19F NMR spectroscopy to quantify the contribution of viscosity, weak interactions, and sample inhomogeneity to resonance broadening in cells. We found that the viscosity in oocytes is only about 1.2 times that of water, and that inhomogeneous broadening is a major factor in determining line width in these cells. [ABSTRACT FROM AUTHOR]

The Ca2+-mediated conformational transition of the protein calmodulin (CaM) is essential to a variety of signal transduction pathways. Whether the transition in living cells is similar to that observed in buffer is not known. Here, we report the direct observation by 19F NMR spectroscopy of the transition of the Ca2+-free and -bound forms in Xenopus laevis oocytes at different Ca2+ levels. We find that the Ca2+-bound CaM population increased greatly upon binding the target protein myosin light-chain kinase (MLCK) at the same Ca2+ level. Paramagnetic NMR spectroscopy was also exploited for the first time to obtain long-range structural constraints in cells. Our study shows that 19F NMR spectroscopy can be used to obtain long-range structural constraints in living eukaryotic cells and paves the way for quantification of protein binding constants. [ABSTRACT FROM AUTHOR]

NMR Spectroscopy In their Communication on page 8686 ff., C. Li et al., demonstrate that 19F labeling is a good first choice for studying globular and disordered proteins in Xenopus oocytes, especially compared with conventional 15N ‐ or 13C ‐ methyl enrichment. By using 19F labeling, they found that, unlike E. coli cells, the viscosity in oocytes is only about 1.2 times that of water and that inhomogeneous broadening contributes 60 – 70 % to the line width. The labeling strategies and resonance broadening mechanisms in Xenopus oocytes were explored with the goal of expanding the application of this cell type. [ABSTRACT FROM AUTHOR]

Protein methylation is crucial in epigenetics, and targeting the involved methyltransferases shows great potential for therapeutic intervention with several inhibitors in clinical trials for oncology indications. Therefore, characterization of protein methylation is essential for understanding the methyltransferase function and discovering chemical inhibitors and antagonists. While NMR has been used to measure methylation rates, isotopic labeling of protein or methyl donors can be costly and cannot characterize demethylation of proteins extracted from natural sources. Our method employs a four-quantum filter 1H-13C experiment that selectively detects methyl groups, providing a simple way to characterize methylation and demethylation features of methyltransferases and demethylases, respectively, without requiring isotopic labeling. In our experiments, we successfully observed the methylation of H3 under lysate from various cells and tissues of mice with cancerous growth. The results revealed that H3 undergoes both mono- and dimethylation in all the tested lysates, but at varying rates and degrees. Significantly lower H3 methylation rates and levels were observed in both cervical tumor and breast tumor lysates compared with the corresponding cancerous cells and healthy cells lysates. These findings highlight the variability of histone H3 methylation patterns among healthy cells, cancerous cells, tumor tissues, and different tumor types, and suggest that this method has great potential in facilitating the development of effective interventions against these diseases. By characterizing the methylation features of suspected tumors or areas of concern, it provides valuable insights into the underlying mechanisms of cancer development and aids in identifying potential targets for therapeutic interventions. [Display omitted] • A novel NMR method to monitor protein methylation and demethylation without isotopic labeling. • The method can be used to monitor methylation kinetics of H3 under lysates from various cells and tissues. • The method provides different metabolism pathways of SAM, and offers potential help for drug development and treatment. [ABSTRACT FROM AUTHOR]

A protein gel electrophoresis procedure using 0.05% w/v sarkosyl, is reported. The method called 05SAR-PAGE can be used to identify the native masses, dimeric states and modification states of proteins, and also be suitable for pursuing native electroblotting and immunodetection. It has been demonstrated by NMR spectroscopy that 0.05% w/v SAR is much milder than SDS, so it has subtle effects on the native structure of proteins. Therefore, the non-covalent dimerization of PhoB N and PhoR cp can be identified by 05SAR-PAGE which cannot be observed by SDS-PAGE. It has also been demonstrated that 05SAR-PAGE can be used to identify the phosphorylated or methylated proteins. Besides, 05SAR-PAGE shows the advantages of simple operation and low cost, and can be easily adapted to diverse applications. Image 1 • Determination of the dimerization states of PhoB N and PhoR cp by 05SAR-PAGE. • Mild effect of SAR on protein structure. • Western-blot of monomer and dimer states in vivo by 05SAR-PAGE. • Identification of different modification states of proteins by 05SAR-PAGE. [ABSTRACT FROM AUTHOR]

The TG interacting factor-1 homeodomain (TGIF1-HD) binds with the consensus DNA motif 5′-TGTCA-3′ in gene promoters through its three-amino acid loop extension (TALE) type homeodomain, and then recruits co-regulators to regulate gene expression. Although the solution NMR structure of human TGIF1-HD has been reported previously, little is known about its DNA binding mechanism. NMR titrations have been extensively used to study mechanisms of ligand binding to target proteins; however, an intermediate exchange occurred predominantly between TGIF1-HD in the free and bound states when titrated with the consensus DNA, which resulted in poor-quality NMR spectra and precluded further exploration of its interaction interface and conformational dynamics. Here, the helix α3 of TGIF1-HD was speculated as the specific DNA binding interface by hydrogen–deuterium exchange mass spectrometry (HDX-MS) experiments, and subsequently confirmed by chemical exchange saturation transfer (CEST) spectroscopy. In addition, simultaneous conformational changes in other regions, including α1 and α2, were induced by DNA binding, explaining the observation of chemical shift perturbations from extensive residues besides those located in α3. Further, low-populated DNA-bound TGIF1-HD undergoing a slow exchange at a rate of 130.2 ± 3.6 s −1 was derived from the analysis of the CEST data, and two residues, R220 and R221, located in the middle of α3 were identified to be crucial for DNA binding. Our study provides structural and dynamic insights into the mechanisms of TGIF1-HD recognition of extensive promoter DNA. [ABSTRACT FROM AUTHOR]