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Brahma R, Raghuraman H. Cost-effective Purification of Membrane Proteins using a Dual-detergent Strategy. Curr Protoc 2022; 2:e452. [PMID: 35714356 PMCID: PMC7614515 DOI: 10.1002/cpz1.452] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Understanding the mechanisms of membrane protein function is critical for biomedical research and drug discovery as membrane proteins constitute ∼30% of the proteins encoded by the genomes of both lower and higher organisms and are targets for two-thirds of approved drugs worldwide. Significant progress has been made in engineering host expression systems for large-scale production of membrane proteins and in determining their three-dimensional high-resolution structures. Despite these efforts, the study of membrane proteins at the atomic level is challenging due to poor expression and extraction, low yields of functional protein, and the complexity and heterogeneity of source membranes. Structural and spectroscopic studies of any membrane protein require that the protein be extracted from its native membranes into a membrane-mimetic stable environment, which is often achieved by the use of detergents. Unfortunately, there is no magic detergent that can extract all membrane proteins and successful extraction often requires a thorough screen of detergents. Furthermore, membrane protein purification in general and the detergents used are very expensive, which puts a financial constraint on sophisticated membrane protein studies. To overcome this hurdle, a dual-detergent strategy has recently been developed and successfully applied to purify various classes of pure, stable, and functionally relevant membrane proteins in a cost-effective manner. This strategy uses an inexpensive detergent for solubilization of the desired protein from membranes and a second detergent during protein purification. In the Basic Protocol, we describe the dual-detergent strategy to significantly reduce the overall purification cost of a bacterial membrane protein using the magnesium ion channel MgtE as an example. Support Protocols are also provided for selecting a suitable E. coli strain for protein expression and the optimal detergent(s) for membrane protein solubilization. © 2022 Wiley Periodicals LLC. Basic Protocol: Expression, membrane solubilization, and cost-effective purification of MgtE Support Protocol 1: Selecting a suitable E. coli strain for optimal protein expression Support Protocol 2: Identification of suitable detergents for membrane protein solubilization.
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Affiliation(s)
- Rupasree Brahma
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Bidhannagar, Kolkata, India.,Homi Bhabha National Institute, Anushaktinagar, Mumbai, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Bidhannagar, Kolkata, India.,Homi Bhabha National Institute, Anushaktinagar, Mumbai, India
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Brahma R, Raghuraman H. Measuring Membrane Penetration Depths and Conformational Changes in Membrane Peptides and Proteins. J Membr Biol 2022; 255:469-483. [PMID: 35274157 DOI: 10.1007/s00232-022-00224-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 02/23/2022] [Indexed: 10/18/2022]
Abstract
The structural organization and dynamic nature of the biomembrane components are important determinants for numerous cellular functions. Particularly, membrane proteins are critically important for various physiological functions and are important drug targets. The mechanistic insights on the complex functionality of membrane lipids and proteins can be elucidated by understanding the interplay between structure and dynamics. In this regard, membrane penetration depth represents an important parameter to obtain the precise depth of membrane-embedded molecules that often define the conformation and topology of membrane probes and proteins. In this review, we discuss about the widely used fluorescence quenching-based methods (parallax method, distribution analysis, and dual-quencher analysis) to accurately determine the membrane penetration depths of fluorescent probes that are either membrane-embedded or attached to lipids and proteins. Further, we also discuss a relatively novel fluorescence quenching method that utilizes tryptophan residue as the quencher, namely the tryptophan-induced quenching, which is sensitive to monitor small-scale conformational changes (short distances of < 15 Å) and useful in mapping distances in proteins. We have provided numerous examples for the benefit of readers to appreciate the importance and applicability of these simple yet powerful methods to study membrane proteins.
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Affiliation(s)
- Rupasree Brahma
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, 1/AF, Bidhannagar, Kolkata, 700 064, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, 1/AF, Bidhannagar, Kolkata, 700 064, India.
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Site-directed fluorescence approaches to monitor the structural dynamics of proteins using intrinsic Trp and labeled with extrinsic fluorophores. STAR Protoc 2022; 3:101200. [PMID: 35252885 PMCID: PMC8889417 DOI: 10.1016/j.xpro.2022.101200] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Comprehensive understanding of a protein’s function depends on having reliable, sophisticated tools to study protein structural dynamics in physiologically-relevant conditions. Here, we present an effective, robust step-by-step protocol to monitor the structural dynamics (including hydration dynamics) of a protein utilizing various site-directed fluorescence (SDFL) approaches. This protocol should be widely applicable for studying soluble proteins, intrinsically-disordered proteins, and membrane proteins. For complete details on the use and execution of this protocol, please refer to Das et al. (2020), Das and Raghuraman (2021), and Chatterjee et al. (2021). A step-by-step protocol to monitor the structural dynamics of proteins using SDFL Applicable to proteins with intrinsic Trp and labeled with extrinsic fluorophores This protocol should be widely applicable for soluble and membrane proteins
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Das A, Bysack A, Raghuraman H. Effectiveness of dual-detergent strategy using Triton X-100 in membrane protein purification. Biochem Biophys Res Commun 2021; 578:122-128. [PMID: 34560581 DOI: 10.1016/j.bbrc.2021.09.031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 09/16/2021] [Indexed: 11/27/2022]
Abstract
Membrane solubilization by detergents is a critical step for successful membrane protein purification. Alkyl maltoside detergents such as DDM and DM are very expensive and are commonly used to produce most of the high-quality proteins in stable and functional form. Recently, dual-detergent strategy using inexpensive detergents for membrane solubilization step has been shown to be highly effective in purifying different classes of membrane proteins in a cost-effective manner. In this work, we have monitored the effectiveness of 'dual-detergent strategy' towards successful purification of the isolated voltage sensing domain (VSD) of KvAP and the inward rectifying K+ channel, KirBac1.1. We demonstrate that the inexpensive detergent Triton X-100 extracts the activated conformation of the KvAP-VSD well without compromising the structural integrity of the sensor, and also retains its proper structural dynamics. Importantly, the cost associated with solubilizing the KvAP sensor can be reduced by ∼2000 fold. To the best of our knowledge, our results constitute the first report characterizing the purification of KvAP voltage sensor using an inexpensive detergent. However, the dual-detergent strategy using Triton X-100 for membrane solubilization is not effective for the purification of inward rectifying K+ channel, KirBac1.1 even in presence of high salt concentration during solubilization. We propose that the dual-detergent strategy will be useful for extracting stable and functional proteins that are both DDM- and DM-extractable, but will be ineffective if the protein is only DM-extractable. The relevance of the effectiveness of dual-detergent strategy with respect to the hydrophobic thickness of proteins is discussed.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, 700 064, India
| | - Arpan Bysack
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, 700 064, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, 700 064, India.
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Novel insights in linking solvent relaxation dynamics and protein conformations utilizing red edge excitation shift approach. Emerg Top Life Sci 2021; 5:89-101. [PMID: 33416893 DOI: 10.1042/etls20200256] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 12/14/2020] [Accepted: 12/18/2020] [Indexed: 01/01/2023]
Abstract
Protein hydration dynamics plays an important role in many physiological processes since protein fluctuations, slow solvation, and the dynamics of hydrating water are all intrinsically related. Red edge excitation shift (REES) is a unique and powerful wavelength-selective (i.e. excitation-energy dependent) fluorescence approach that can be used to directly monitor the environment-induced restriction and dynamics around a polar fluorophore in a complex biological system. This review is mainly focused on recent applications of REES and a novel analysis of REES data to monitor the structural dynamics, functionally relevant conformational transitions and to unmask the structural ensembles in proteins. In addition, the novel utility of REES in imaging protein aggregates in a cellular context is discussed. We believe that the enormous potential of REES approach showcased in this review will engage more researchers, particularly from life sciences.
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Chatterjee S, Brahma R, Raghuraman H. Gating-related Structural Dynamics of the MgtE Magnesium Channel in Membrane-Mimetics Utilizing Site-Directed Tryptophan Fluorescence. J Mol Biol 2020; 433:166691. [PMID: 33203509 DOI: 10.1016/j.jmb.2020.10.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 10/17/2020] [Accepted: 10/19/2020] [Indexed: 12/25/2022]
Abstract
Magnesium is the most abundant divalent cation present in the cell, and an abnormal Mg2+ homeostasis is associated with several diseases in humans. However, among ion channels, the mechanisms of intracellular regulation and transport of Mg2+ are poorly understood. MgtE is a homodimeric Mg2+-selective channel and is negatively regulated by high intracellular Mg2+ concentration where the cytoplasmic domain of MgtE acts as a Mg2+ sensor. Most of the previous biophysical studies on MgtE have been carried out in detergent micelles and the information regarding gating-related structural dynamics of MgtE in physiologically-relevant membrane environment is scarce. In this work, we monitored the changes in gating-related structural dynamics, hydration dynamics and conformational heterogeneity of MgtE in micelles and membranes using the intrinsic site-directed Trp fluorescence. For this purpose, we have engineered six single-Trp mutants in the functional Trp-less background of MgtE to obtain site-specific information on the gating-related structural dynamics of MgtE in membrane-mimetic systems. Our results indicate that Mg2+-induced gating might involve the possibility of a 'conformational wave' from the cytosolic N-domain to transmembrane domain of MgtE. Although MgtE is responsive to Mg2+-induced gating in both micelles and membranes, the organization and dynamics of MgtE is substantially altered in physiologically important phospholipid membranes compared to micelles. This is accompanied by significant changes in hydration dynamics and conformational heterogeneity. Overall, our results highlight the importance of lipid-protein interactions and are relevant for understanding gating mechanism of magnesium channels in general, and MgtE in particular.
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Affiliation(s)
- Satyaki Chatterjee
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - Rupasree Brahma
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India.
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Raghuraman H, Chatterjee S, Das A. Site-Directed Fluorescence Approaches for Dynamic Structural Biology of Membrane Peptides and Proteins. Front Mol Biosci 2019; 6:96. [PMID: 31608290 PMCID: PMC6774292 DOI: 10.3389/fmolb.2019.00096] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 09/11/2019] [Indexed: 12/31/2022] Open
Abstract
Membrane proteins mediate a number of cellular functions and are associated with several diseases and also play a crucial role in pathogenicity. Due to their importance in cellular structure and function, they are important drug targets for ~60% of drugs available in the market. Despite the technological advancement and recent successful outcomes in determining the high-resolution structural snapshot of membrane proteins, the mechanistic details underlining the complex functionalities of membrane proteins is least understood. This is largely due to lack of structural dynamics information pertaining to different functional states of membrane proteins in a membrane environment. Fluorescence spectroscopy is a widely used technique in the analysis of functionally-relevant structure and dynamics of membrane protein. This review is focused on various site-directed fluorescence (SDFL) approaches and their applications to explore structural information, conformational changes, hydration dynamics, and lipid-protein interactions of important classes of membrane proteins that include the pore-forming peptides/proteins, ion channels/transporters and G-protein coupled receptors.
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Affiliation(s)
- H. Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
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Das A, Chatterjee S, Raghuraman H. Structural Dynamics of the Paddle Motif Loop in the Activated Conformation of KvAP Voltage Sensor. Biophys J 2019; 118:873-884. [PMID: 31547975 DOI: 10.1016/j.bpj.2019.08.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 07/31/2019] [Accepted: 08/06/2019] [Indexed: 02/07/2023] Open
Abstract
Voltage-dependent potassium (Kv) channels play a fundamental role in neuronal and cardiac excitability and are potential therapeutic targets. They assemble as tetramers with a centrally located pore domain surrounded by a voltage-sensing domain (VSD), which is critical for sensing transmembrane potential and subsequent gating. Although the sensor is supposed to be in "Up" conformation in both n-octylglucoside (OG) micelles and phospholipid membranes in the absence of membrane potential, toxins that bind VSD and modulate the gating behavior of Kv channels exhibit dramatic affinity differences in these membrane-mimetic systems. In this study, we have monitored the structural dynamics of the S3b-S4 loop of the paddle motif in activated conformation of KvAP-VSD by site-directed fluorescence approaches, using the environment-sensitive fluorescent probe 7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine (NBD). Emission maximum of NBD-labeled loop region of KvAP-VSD (residues 110-117) suggests a significant change in the polarity of local environment in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) membranes compared to OG micelles. This indicates that S3b-S4 loop residues might be partitioning to membrane interface, which is supported by an overall increased mean fluorescence lifetimes and significantly reduced water accessibility in membranes. Further, the magnitude of red edge excitation shift (REES) supports the presence of restricted/bound water molecules in the loop region of the VSD in micelles and membranes. Quantitative analysis of REES data using Gaussian probability distribution function clearly indicates that the sensor loop has fewer discrete equilibrium conformational states when reconstituted in membranes. Interestingly, this reduced molecular heterogeneity is consistent with the site-specific NBD polarization results, which suggest that the membrane environment offers a relaxed/dynamic organization for most of the S3b-S4 loop residues of the sensor. Overall, our results are relevant for understanding toxin-VSD interaction and gating mechanisms of Kv channels in membranes.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - Satyaki Chatterjee
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India.
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