Current Protocols in Protein Science最新文献

Cover: In Wolfe et al. (https://doi.org/10.1002/cpps.96), Representative two phases of the isothermal detergent desorption of membrane proteins. (A) The initial phase is detergent predesolvation. (B) The follow-up, time-dependent phase is detergent desolvation. Predesolvation results from the dissociation of a relatively small number of detergent monomers from membrane proteins. This process is accompanied by a relatively small and slow change in the FP anisotropy with respect to the initial value, rmax. The second phase depicts a large and fast alteration in the FP anisotropy, as it is representative of the loss of many detergent monomers from membrane proteins. This major change in the average molecular mass of proteomicelles is reflected in a drastic alteration of the FP anisotropy, and occurs in a single-exponential fashion (right-hand panels). The kinetic rates of both predesolvation and desolvation phases are dependent on the final detergent concentration (Wolfe et al., 2018a). For example, the kinetic rates are greater for lower detergent concentrations in the protein sample. Reprinted with permission from reference Wolfe et al. (2018b). Copyright 2018, American Chemical Society.

Glycans are a class of macromolecules essential for all forms of life. They embellish various proteins and other macromolecules in organisms and are responsible for their proper functioning. Because their complex structure is determined by genetic and environmental factors, analysis of such molecules is rather demanding. Liquid chromatography (high-performance and ultra-performance, HPLC and UPLC, respectively) analysis has been used for the purpose of glycoprofiling for years and it is a well-established method regarding its robustness, reproducibility, and high throughput. Another orthogonal method that is now used in glycoprofiling is capillary gel electrophoresis (CGE) because it offers powerful separation and distinct sensitivity. The purpose of the following protocols is to present all steps required for release and fluorescent labeling of total N-glycans from blood plasma/serum or isolated glycoprotein (for example, IgG) and their subsequent UPLC or CGE analysis. © 2019 by John Wiley & Sons, Inc.

This article provides detailed protocols for a high-throughput fluorescence polarization (FP) spectroscopy approach to disentangle the interactions of membrane proteins with solubilizing detergents. Existing techniques for examining the membrane protein-detergent complex (PDC) interactions are low throughput and require high amounts of proteins. Here, we describe a 96-well analytical approach, which facilitates a scalable analysis of the PDC interactions at low-nanomolar concentrations of membrane proteins in native solutions. At detergent concentrations much greater than the equilibrium dissociation constant of the PDC, K_d, the FP anisotropy reaches a saturated value, so it is independent of the detergent concentration. On the contrary, at detergent concentrations comparable with or lower than the K_d, the FP anisotropy readout undergoes a time-dependent decrease, exhibiting a sensitive and specific detergent-dissociation signature. Our approach can also be used for determining the kinetic rate constants of association and dissociation. With further development, these protocols might be used in various arenas of membrane protein research that pertain to extraction, solubilization, and stabilization. © 2019 by John Wiley & Sons, Inc.

Site- and structure-specific quantitative N-glycoproteomics characterization of differentially expressed N-glycosylation at the intact N-glycopeptide level with distinct chromatographic separation and structure-specific fragment ions has become possible with the recent development of RPLC-pentaHILIC 2DLC separation and use of the intact N-glycopeptide search engine GPSeeker. Here we provide a detailed protocol for this GPSeeker-centered structure-specific isotopic-labeling quantitative N-glycoproteomics pipeline. The protocols include sample preparation of a 1:1 mixture of light (-CH₃)₂ and heavy (-¹³CD₂H)₂ dimethylated intact N-glycopeptides from LO2 and HepG2 cells, RPLC-pentaHILIC 2DLC separation of the mixture, intact N-glycopeptide database search and identification using GPSeeker, and quantitation of differentially expressed intact N-glycopeptides using the quantitation module GPSeekerQuan. © 2019 by John Wiley & Sons, Inc.

Heterologous expression of the G protein–coupled estrogen receptor (GPER) comes with a suite of challenges intrinsic to membrane proteins. This receptor's low expression levels and tendency to form insoluble aggregates in Escherichia coli and yeast make it a difficult receptor-target to study. In this unit, we detail steps to produce monomeric GPER using a precipitation-based cell-free system. We provide information on the DNA construct for expression, the pipetting scheme for the reaction supplements to generate a master mix, and the cell-free reaction setup. In the last portion of this unit, we outline steps for solubilization and purification, and we provide a viable method for qualitatively observing functionality by liquid chromatography–mass spectrometry detection. © 2019 by John Wiley & Sons, Inc.

Cover: In Adelmant et al. (https://doi.org/10.1002/cpps.84), Overview of the Basic Protocols described in this article. See e84.

This article describes processing of protein samples using 1D SDS gels prior to protease digestion for proteomics workflows that subsequently utilize reversed-phase nanocapillary ultra-high-pressure liquid chromatography (LC) coupled to tandem mass spectrometry (MS/MS). The resulting LC-MS/MS data are used to identify peptides and thereby infer proteins present in samples ranging from simple mixtures to very complex proteomes. Bottom-up proteome studies usually involve quantitative comparisons across several or many samples. For either situation, 1D SDS gels represent a simple, widely available technique that can be used to either fractionate complex proteomes or rapidly clean up low microgram samples with minimal losses. After gel separation and staining/destaining, appropriate gel slices are excised, and in-gel reduction, alkylation, and protease digestion are performed. Digests are then processed for LC-MS/MS analysis. Protocols are described for either sample fractionation with high-throughput processing of many samples or simple cleanup without fractionation. An optional strategy is to conduct in-solution reduction and alkylation prior to running gels, which is advantageous when a large number of samples will be separated into large numbers of fractions. Optimization of trypsin digestion parameters and comparison to in-solution protease digestion are also described. © 2019 by John Wiley & Sons, Inc.

This manuscript describes protocols for separation of complex protein samples using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Electrophoresis in a single dimension, e.g., 1D SDS polyacrylamide gels, has the potential to rapidly separate hundreds of proteins. When two orthogonal high-resolution electrophoretic methods are efficiently combined in perpendicular dimensions, complex protein mixtures can be separated into thousands of discrete spots. The most common 2D gel separation for intact proteins involves a first-dimensional separation using isoelectric focusing (IEF) followed by separation based on protein size (SDS-PAGE). Currently, most 2D gel studies rely on the use of commercially available immobilized pH gradient (IPG) gels, which provide improved ease of use and reproducibility compared with older methods. IPG gels are available in a range of sizes and different pH ranges. Resolution typically increases as the 2D gel size increases; however, difficulty of use increases sharply and throughput decreases as gel size increases. © 2019 by John Wiley & Sons, Inc.

The formation of disulfide bonds in proteins is an important post-translational modification that is critical for stabilizing the native structures of proteins, particularly proteins exposed to oxidizing environments. For this reason, most cysteines in secreted proteins or protein domains on the surface of the cell are in disulfides, whereas most cysteines in the cytoplasm are in the unmodified -SH form. Disulfide linkages must be experimentally determined, as they cannot be predicted from amino acid sequence. These assignments provide insights into three-dimensional structure and contribute to the understanding of structural-functional relationships. This unit details a series of protocols that have been applied successfully to map disulfide bonds in proteins. The general strategy involves chemical or proteolytic cleavage of the protein followed by chromatographic separation of the resultant peptides. Mass spectrometry is used to identify disulfide-containing peptides and determine sites of disulfide linkage. A partial reduction and alkylation strategy for mapping disulfide linkages in peptides with multiple disulfide bonds is also presented. © 2019 by John Wiley & Sons, Inc.

Affinity purification followed by mass spectrometry has become the technique of choice to identify binding partners in biochemical complexes isolated from a physiologic cellular context. In this report we detail our protocol for tandem affinity purification (TAP) primarily based on the use of the FLAG and HA peptide epitopes, with a particular emphasis on factors affecting yield and specificity, as well as steps to implement an automated version of the TAP procedure. © 2019 by John Wiley & Sons, Inc.