发布: 2018年09月05日第8卷第17期 DOI: 10.21769/BioProtoc.2470 浏览次数: 5976
评审: Anonymous reviewer(s)
Abstract
Substituted Cysteine Accessibility Method (SCAM) is a biochemical approach to investigate the water accessibility or the spatial distance of particular cysteine residues substituted in the target protein. Protein topology and structure can be annotated by labeling with methanethiosulfonate reagents that specifically react with the cysteine residues facing the hydrophilic environment, even within the transmembrane domain. Cysteine crosslinking experiments provide us with information about the distance between two cysteine residues. The combination of these methods enables us to obtain information about the structural changes of the target protein. Here, we describe the detailed protocol for structural analysis using SCAM.
Keywords: Cysteine (半胱氨酸)Background
Structural analyses provide the critical information about the function of a target protein. X-ray crystallography and nuclear magnetic resonance have been utilized as high-resolution protein structural analysis methods in the biology field. However, these methods require a purified protein extracted from membrane at very high concentration for the structural analysis of membrane proteins. Substituted Cysteine Accessibility Method (SCAM) is a biochemical approach to analyze the water accessibility and the spatial distance of particular cysteine residues substituted in the target protein. Using methanethiosulfonate (MTS) reagents that specifically react with the cysteine residues facing the hydrophilic environment, we can annotate the topology and structure of the target protein. As the labeling reagent N-biotinylaminoethyl methanethiosulfonate (MTSEA-biotin) is impermeable to the plasma membrane (Seal et al., 1998), in intact cells, only extracellular, but not intracellular, cysteine residues are biotinylated (Figure 1A). In contrast, both extracellular and intracellular cysteine residues are exposed to the hydrophilic environment in microsomes and are biotinylated by MTSEA-biotin (Figure 1B). Moreover, the accessibility of cysteine can be analyzed by competition experiments using membrane-impermeable MTS derivatives (Figure 2A). By combining the results of these analyses, we are able to obtain structural information of the entire intrinsic protein in the membrane (Akabas et al., 1992; Loo and Clarke, 1995; Frillingos et al., 1998; Karlin and Akabas, 1998; Foucaud et al., 2001; Kaback et al., 2001; Bogdanov et al., 2005; Sato et al., 2006 and 2008; Takagi et al., 2010; Watanabe et al., 2010; Takagi-Niidome et al., 2015; Tominaga et al., 2016; Cai et al., 2017; Tomita, 2017). The accessibility of cysteine can be analyzed in more detail by competition experiments using membrane-impermeable MTS derivatives; the negatively charged 2-sulfonatoethyl methanethiosulfonate (MTSES), the positively charged 2-(trimethylammonium)-ethyl methanethiosulfonate (MTSET), and the sterically bulkiest 2-(Triethylammonium)-Ethyl Methanethiosulfonate Bromide (MTS-TEAE) (Figure 2A). Moreover, cross-linking experiments using microsome fractions provide information regarding the spatial distance between two separated cysteines in different polypeptides (Figure 3A) (Loo and Clarke, 1996; 2000; 2001; Klco et al., 2003). In this experiment, all endogenous cysteines of the target protein should be mutated by serine or alanine (cys-less mutant), and then one (single cys-mutation) or two (double cys-mutation) target residues would be substituted to the cysteine to analyze the accessibility of particular residue(s) by MTS reagents. However, sometimes these substitutions affect the structure and function of the target protein. Thus, it is important to analyze the biological function of the target protein to ensure whether the mutations do not affect the protein conformation.
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© 2018 The Authors; exclusive licensee Bio-protocol LLC.
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分类
生物化学 > 蛋白质 > 结构
生物化学 > 蛋白质 > 活性
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