1
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Mensah GAK, Schaefer KG, Roberts AG, King GM, Bartlett MG. Probing the Mechanisms Underlying the Transport of the Vinca Alkaloids by P-glycoprotein. J Pharm Sci 2024; 113:1960-1974. [PMID: 38527618 DOI: 10.1016/j.xphs.2024.03.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 03/18/2024] [Accepted: 03/18/2024] [Indexed: 03/27/2024]
Abstract
The efficacy of many cancer drugs is hindered by P-glycoprotein (Pgp), a cellular pump that removes drugs from cells. To improve chemotherapy, drugs capable of evading Pgp must be developed. Despite similarities in structure, vinca alkaloids (VAs) show disparate Pgp-mediated efflux ratios. ATPase activity and binding affinity studies show at least two binding sites for the VAs: high- and low-affinity sites that stimulate and inhibit the ATPase activity rate, respectively. The affinity for ATP from the ATPase kinetics curve for vinblastine (VBL) at the high-affinity site was 2- and 9-fold higher than vinorelbine (VRL) and vincristine (VCR), respectively. Conversely, VBL had the highest Km (ATP) for the low-affinity site. The dissociation constants (KDs) determined by protein fluorescence quenching were in the order VBL < VRL< VCR. The order of the KDs was reversed at higher substrate concentrations. Acrylamide quenching of protein fluorescence indicate that the VAs, either at 10 µM or 150 µM, predominantly maintain Pgp in an open-outward conformation. When 3.2 mM AMPPNP was present, 10 µM of either VBL, VRL, or VCR cause Pgp to shift to an open-outward conformation, while 150 µM of the VAs shifted the conformation of Pgp to an intermediate orientation, between opened inward and open-outward. However, the conformational shift induced by saturating AMPPNP and VCR condition was less than either VBL or VRL in the presence of AMPPNP. At 150 µM, atomic force microscopy (AFM) revealed that the VAs shift Pgp population to a predominantly open-inward conformation. Additionally, STDD NMR studies revealed comparable groups in VBL, VRL, and VCR are in contact with the protein during binding. Our results, when coupled with VAs-microtubule structure-activity relationship studies, could lay the foundation for developing next-generation VAs that are effective as anti-tumor agents. A model that illustrates the intricate process of Pgp-mediated transport of the VAs is presented.
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Affiliation(s)
- Gershon A K Mensah
- Department of Pharmaceutical and Biomedical Science, University of Georgia, Athens, GA 30602, USA
| | - Katherine G Schaefer
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
| | - Arthur G Roberts
- Department of Pharmaceutical and Biomedical Science, University of Georgia, Athens, GA 30602, USA.
| | - Gavin M King
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA; Joint with Biochemistry, University of Missouri, Columbia, MO 65211, USA.
| | - Michael G Bartlett
- Department of Pharmaceutical and Biomedical Science, University of Georgia, Athens, GA 30602, USA.
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2
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Nguyen PH, Cui S, Kozarich AM, Rautio A, Roberts AG, Xiong MP. Utilizing surface plasmon resonance as a novel method for monitoring in-vitro P-glycoprotein efflux. FRONTIERS IN BIOPHYSICS 2024; 2:1367511. [PMID: 38645731 PMCID: PMC11027885 DOI: 10.3389/frbis.2024.1367511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
P-glycoprotein (Pgp) is known for its dichotomous roles as both a safeguarding efflux transporter against xenobiotics and as a catalyst for multidrug resistance. Given the susceptibility of numerous therapeutic compounds to Pgp-mediated resistance, compliance with Food and Drug Administration (FDA) guidelines mandates an in-depth in vitro transport assay during drug development. This study introduces an innovative transport assay that aligns with these regulatory imperatives but also addresses limitations in the currently established techniques. Using Pgp-reconstituted liposomes and employing surface plasmon resonance (SPR), this study developed a distinct method of measuring the relative transport rates of Pgp substrates in a controlled microenvironment. The Pgp substrates selected for this study-quinidine, methadone, and desipramine-resulted in transport ratios that corroborate with trends previously observed. To assess the kinetics of Pgp-mediated transport, the results were analyzed by fitting the data to both currently proposed Pgp substrate translocation models-the vacuum cleaner and flippase models. While the resulting kinetic analysis in this study lends support predominantly to the vacuum cleaner model, this study most notably developed a novel method of assessing Pgp-mediated transport rates and real-time kinetics using surface plasmon resonance.
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Affiliation(s)
- Phuong H. Nguyen
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, United States
| | - Shuolin Cui
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, United States
| | - Amanda M. Kozarich
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, United States
| | - Alex Rautio
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, United States
| | - Arthur G. Roberts
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, United States
| | - May P. Xiong
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, United States
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3
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Weaver DR, Schaefer KG, King GM. Atomic force microscope kymograph analysis: A case study of two membrane proteins. Methods 2024; 223:83-94. [PMID: 38286332 DOI: 10.1016/j.ymeth.2024.01.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 01/09/2024] [Accepted: 01/10/2024] [Indexed: 01/31/2024] Open
Abstract
Kymograph analysis is employed across the biological atomic force microscopy (AFM) community to boost temporal resolution. The method is well suited for revealing protein dynamics at the single molecule level in near-native conditions. Yet, kymograph analysis comes with limitations that depend on several factors including protein geometry and instrumental drift. This work focuses on conformational dynamics of difficult-to-study sparse distributions of membrane proteins. We compare and contrast AFM kymograph analysis for two proteins, one of which (SecDF) exhibits conformational dynamics primarily in the vertical direction (normal to the membrane surface) and the other (Pgp) exhibits a combination of lateral dynamics and vertical motion. Common experimental issues are analyzed including translational and rotational drift. Conformational transition detection is evaluated via kymograph simulations followed by state detection algorithms. We find that kymograph analysis is largely robust to lateral drift. Displacement of the AFM line scan trajectory away from the protein center of mass by a few nanometers, roughly half of the molecule diameter, does not significantly affect transition detection nor generate undue dwell time errors. On the other hand, for proteins like Pgp that exhibit significant azimuthal maximum height dependence, rotational drift can potentially produce artifactual transitions. Measuring the height of a membrane protein protrusion is generally superior to measurement of width, confirming intuition based on vertical resolution superiority. In low signal-to-noise scenarios, common state detection algorithms struggle with transition detection as opposed to infinite hidden Markov models. AFM kymography represents a valuable addition to the membrane biophysics toolkit; continued hardware and software improvements are poised to expand the method's impact in the field.
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Affiliation(s)
- Dylan R Weaver
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia MO 65211 USA
| | - Katherine G Schaefer
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia MO 65211 USA
| | - Gavin M King
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia MO 65211 USA; Joint with Department of Biochemistry, University of Missouri-Columbia, Columbia MO 65211 USA.
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4
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Mensah GAK, Schaefer KG, Bartlett MG, Roberts AG, King GM. Drug-Induced Conformational Dynamics of P-Glycoprotein Underlies the Transport of Camptothecin Analogs. Int J Mol Sci 2023; 24:16058. [PMID: 38003248 PMCID: PMC10671697 DOI: 10.3390/ijms242216058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 10/24/2023] [Accepted: 10/28/2023] [Indexed: 11/26/2023] Open
Abstract
P-glycoprotein (Pgp) plays a pivotal role in drug bioavailability and multi-drug resistance development. Understanding the protein's activity and designing effective drugs require insight into the mechanisms underlying Pgp-mediated transport of xenobiotics. In this study, we investigated the drug-induced conformational changes in Pgp and adopted a conformationally-gated model to elucidate the Pgp-mediated transport of camptothecin analogs (CPTs). While Pgp displays a wide range of conformations, we simplified it into three model states: 'open-inward', 'open-outward', and 'intermediate'. Utilizing acrylamide quenching of Pgp fluorescence as a tool to examine the protein's tertiary structure, we observed that topotecan (TPT), SN-38, and irinotecan (IRT) induced distinct conformational shifts in the protein. TPT caused a substantial shift akin to AMPPNP, suggesting ATP-independent 'open-outward' conformation. IRT and SN-38 had relatively moderate effects on the conformation of Pgp. Experimental atomic force microscopy (AFM) imaging supports these findings. Further, the rate of ATPase hydrolysis was correlated with ligand-induced Pgp conformational changes. We hypothesize that the separation between the nucleotide-binding domains (NBDs) creates a conformational barrier for substrate transport. Substrates that reduce the conformational barrier, like TPT, are better transported. The affinity for ATP extracted from Pgp-mediated ATP hydrolysis kinetics curves for TPT was about 2-fold and 3-fold higher than SN-38 and IRT, respectively. On the contrary, the dissociation constants (KD) determined by fluorescence quenching for these drugs were not significantly different. Saturation transfer double difference (STDD) NMR of TPT and IRT with Pgp revealed that similar functional groups of the CPTs are accountable for Pgp-CPTs interactions. Efforts aimed at modifying these functional groups, guided by available structure-activity relationship data for CPTs and DNA-Topoisomerase-I complexes, could pave the way for the development of more potent next-generation CPTs.
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Affiliation(s)
- Gershon A. K. Mensah
- Department of Pharmaceutical and Biomedical Science, University of Georgia, Athens, GA 30602, USA; (G.A.K.M.)
| | - Katherine G. Schaefer
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA;
| | - Michael G. Bartlett
- Department of Pharmaceutical and Biomedical Science, University of Georgia, Athens, GA 30602, USA; (G.A.K.M.)
| | - Arthur G. Roberts
- Department of Pharmaceutical and Biomedical Science, University of Georgia, Athens, GA 30602, USA; (G.A.K.M.)
| | - Gavin M. King
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA;
- Joint with Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
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5
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Walsh OD, Choi L, Sigdel KP. Effect of CM15 on Supported Lipid Bilayer Probed by Atomic Force Microscopy. MEMBRANES 2023; 13:864. [PMID: 37999350 PMCID: PMC10672887 DOI: 10.3390/membranes13110864] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2023] [Revised: 10/26/2023] [Accepted: 10/26/2023] [Indexed: 11/25/2023]
Abstract
Antimicrobial peptides are key components of the immune system. These peptides affect the membrane in various ways; some form nano-sized pores, while others only produce minor defects. Since these peptides are increasingly important in developing antimicrobial drugs, understanding the mechanism of their interactions with lipid bilayers is critical. Here, using atomic force microscopy (AFM), we investigated the effect of a synthetic hybrid peptide, CM15, on the membrane surface comprising E. coli polar lipid extract. Direct imaging of supported lipid bilayers exposed to various concentrations of the peptide revealed significant membrane remodeling. We found that CM15 interacts with supported lipid bilayers and forms membrane-spanning defects very quickly. It is found that CM15 is capable of remodeling both leaflets of the bilayer. For lower CM15 concentrations, punctate void-like defects were observed, some of which re-sealed themselves as a function of time. However, for CM15 concentrations higher than 5 µM, the defects on the bilayers became so widespread that they disrupted the membrane integrity completely. This work enhances the understanding of CM15 interactions with the bacterial lipid bilayer.
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Affiliation(s)
| | | | - Krishna P. Sigdel
- Department of Physics and Astronomy, California State Polytechnic University, Pomona, CA 91768, USA
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6
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Schaefer KG, Roberts AG, King GM. Advantages and potential limitations of applying AFM kymograph analysis to pharmaceutically relevant membrane proteins in lipid bilayers. Sci Rep 2023; 13:11427. [PMID: 37454132 PMCID: PMC10349840 DOI: 10.1038/s41598-023-37910-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 06/29/2023] [Indexed: 07/18/2023] Open
Abstract
Membrane proteins play critical roles in disease and in the disposition of many pharmaceuticals. A prime example is P-glycoprotein (Pgp) which moves a diverse range of drugs across membranes and out of the cell before a therapeutic payload can be delivered. Conventional structural biology methods have provided a valuable framework for comprehending the complex conformational changes underlying Pgp function, which also includes ATPase activity, but the lack of real-time information hinders understanding. Atomic force microscopy (AFM) is a single-molecule technique that is well-suited for studying active membrane proteins in bilayers and is poised to advance the field beyond static snapshots. After verifying Pgp activity in surface-support bilayers, we used kymograph analysis in conjunction with AFM imaging and simulations to study structural transitions at the 100 ms timescale. Though kymographs are frequently employed to boost temporal resolution, the limitations of the method have not been well characterized, especially for sparse non-crystalline distributions of pharmaceutically relevant membrane proteins like Pgp. Common experimental challenges are analyzed, including protein orientation, instrument noise, and drift. Surprisingly, a lateral drift of 75% of the protein dimension leads to only a 12% probability of erroneous state transition detection; average dwell time error achieves a maximum value of 6%. Rotational drift of proteins like Pgp, with azimuthally-dependent maximum heights, can lead to artifactual transitions. Torsional constraints can alleviate this potential pitfall. Confidence in detected transitions can be increased by adding conformation-altering ligands such as non-hydrolysable analogs. Overall, the data indicate that AFM kymographs are a viable method to access conformational dynamics for Pgp, but generalizations of the method should be made with caution.
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Affiliation(s)
- Katherine G Schaefer
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Arthur G Roberts
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA, 30602, USA.
| | - Gavin M King
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA.
- Joint With Department of Biochemistry, University of Missouri, Columbia, MO, 65211, USA.
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7
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Sun H, Wang J. Novel perspective for protein-drug interaction analysis: atomic force microscope. Analyst 2023; 148:454-474. [PMID: 36398684 DOI: 10.1039/d2an01591a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Proteins are major drug targets, and drug-target interaction identification and analysis are important factors for drug discovery. Atomic force microscopy (AFM) is a powerful tool making it possible to image proteins with nanometric resolution and probe intermolecular forces under physiological conditions. We review recent studies conducted in the field of target protein drug discovery using AFM-based analysis technology, including drug-driven changes in nanomechanical properties of protein morphology and interactions. Underlying mechanisms (including thermodynamic and kinetic parameters) of the drug-target interaction and drug-modulating protein-protein interaction (PPI) on the surfaces of models or living cells are discussed. Furthermore, challenges and the outlook for the field are likewise discussed. Overall, this insight into the mechanical properties of protein-drug interactions provides an unprecedented information framework for rational drug discovery in the pharmaceutical field.
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Affiliation(s)
- Heng Sun
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, 400044, China.
| | - Jianhua Wang
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, 400044, China.
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8
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Roberts AG, Stevens JC, Szklarz GD, Scott EE, Kumar S, Shah MB, Halpert JR. Four Decades of Cytochrome P450 2B Research: From Protein Adducts to Protein Structures and Beyond. Drug Metab Dispos 2023; 51:111-122. [PMID: 36310033 PMCID: PMC11022898 DOI: 10.1124/dmd.122.001109] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/18/2022] [Accepted: 10/20/2022] [Indexed: 01/03/2023] Open
Abstract
This article features selected findings from the senior author and colleagues dating back to 1978 and covering approximately three-fourths of the 60 years since the discovery of cytochrome P450. Considering the vast number of P450 enzymes in this amazing superfamily and their importance for so many fields of science and medicine, including drug design and development, drug therapy, environmental health, and biotechnology, a comprehensive review of even a single topic is daunting. To make a meaningful contribution to the 50th anniversary of Drug Metabolism and Disposition, we trace the development of the research in a single P450 laboratory through the eyes of seven individuals with different backgrounds, perspectives, and subsequent career trajectories. All co-authors are united in their fascination for the structural basis of mammalian P450 substrate and inhibitor selectivity and using such information to improve drug design and therapy. An underlying theme is how technological advances enable scientific discoveries that were impossible and even inconceivable to prior generations. The work performed spans the continuum from: 1) purification of P450 enzymes from animal tissues to purification of expressed human P450 enzymes and their site-directed mutants from bacteria; 2) inhibition, metabolism, and spectral studies to isothermal titration calorimetry, deuterium exchange mass spectrometry, and NMR; 3) homology models based on bacterial P450 X-ray crystal structures to rabbit and human P450 structures in complex with a wide variety of ligands. Our hope is that humanizing the scientific endeavor will encourage new generations of scientists to make fundamental new discoveries in the P450 field. SIGNIFICANCE STATEMENT: The manuscript summarizes four decades of work from Dr. James Halpert's laboratory, whose investigations have shaped the cytochrome P450 field, and provides insightful perspectives of the co-authors. This work will also inspire future drug metabolism scientists to make critical new discoveries in the cytochrome P450 field.
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Affiliation(s)
- Arthur G Roberts
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.).
| | - Jeffrey C Stevens
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.)
| | - Grazyna D Szklarz
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.)
| | - Emily E Scott
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.)
| | - Santosh Kumar
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.)
| | - Manish B Shah
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.)
| | - James R Halpert
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, 240 W. Green St., Athens, Georgia (A.G.R.); Unaffiliated (J.C.S.); Department of Pharmaceutical Sciences, West Virginia University, Morgantown, West Virginia (G.D.S.); Departments of Medicinal Chemistry, Pharmacology, and Biological Chemistry and the Program in Biophysics, University of Michigan, Ann Arbor, Michigan (E.E.S.); Department of Pharmaceutical Sciences, The University of Tennessee Health Science Center, Memphis, Tennessee (S.K.); Department of Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, Albany, New York (M.B.S.); Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, P.O. Box 210207, Tucson, Arizona (J.R.H.)
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9
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Review on the applications of atomic force microscopy imaging in proteins. Micron 2022; 159:103293. [DOI: 10.1016/j.micron.2022.103293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 04/22/2022] [Accepted: 05/06/2022] [Indexed: 11/19/2022]
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10
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Clouser AF, Atkins WM. Long Range Communication between the Drug-Binding Sites and Nucleotide Binding Domains of the Efflux Transporter ABCB1. Biochemistry 2022; 61:730-740. [PMID: 35384651 PMCID: PMC9022228 DOI: 10.1021/acs.biochem.2c00056] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The ABC efflux pump
P-glycoprotein (P-gp) transports a wide variety
of drugs and is inhibited by others. Some drugs stimulate ATP hydrolysis
at the nucleotide binding domains (NBDs) and are transported, others
uncouple ATP hydrolysis and transport, and others inhibit ATP hydrolysis.
The molecular basis for the different behavior of these drugs is not
well understood despite the availability of several structural models
of P-gp complexes with ligands bound. Hypothetically, ligands differentially
alter the conformational dynamics of peptide segments that mediate
the coupling between the drug binding sites and the NBDs. Here, we
explore by hydrogen-deuterium exchange mass spectrometry the dynamic
consequences of a classic substrate and inhibitor, vinblastine and
zosuquidar, binding to mouse P-gp (mdr1a) in lipid nanodiscs. The
dynamics of P-gp in nucleotide-free, pre-hydrolysis, and post-hydrolysis
states in the presence of each drug reveal distinct mechanisms of
ATPase stimulation and implications for transport. For both drugs,
there are common regions affected in a similar manner, suggesting
that particular networks are the key to stimulating ATP hydrolysis.
However, drug binding effects diverge in the post-hydrolysis state,
particularly in the intracellular helices (ICHs 3 and 4) and neighboring
transmembrane helices. The local dynamics and conformational equilibria
in this region are critical for the coupling of drug binding and ATP
hydrolysis and are differentially modulated in the catalytic cycle.
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Affiliation(s)
- Amanda F Clouser
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195-7610, United States
| | - William M Atkins
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195-7610, United States
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11
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Schaefer KG, Pittman AE, Barrera FN, King GM. Atomic force microscopy for quantitative understanding of peptide-induced lipid bilayer remodeling. Methods 2022; 197:20-29. [PMID: 33164792 DOI: 10.1016/j.ymeth.2020.10.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 10/17/2020] [Accepted: 10/20/2020] [Indexed: 12/15/2022] Open
Abstract
A number of peptides are known to bind lipid bilayer membranes and cause these natural barriers to leak in an uncontrolled manner. Though membrane permeabilizing peptides play critical roles in cellular activity and may have promising future applications in the therapeutic arena, significant questions remain about their mechanisms of action. The atomic force microscope (AFM) is a single molecule imaging tool capable of addressing lipid bilayers in near-native fluid conditions. The apparatus complements traditional assays by providing local topographic maps of bilayer remodeling induced by membrane permeabilizing peptides. The information garnered from the AFM includes direct visualization and statistical analyses of distinct bilayer remodeling modes such as highly localized pore-like voids in the bilayer and dispersed thinned membrane regions. Colocalization of distinct remodeling modes can be studied. Here we examine recent work in the field and outline methods used to achieve precise AFM image data. Experimental challenges and common pitfalls are discussed as well as techniques for unbiased analysis including the Hessian blob detection algorithm, bootstrapping, and the Bayesian information criterion. When coupled with robust statistical analyses, high precision AFM data is poised to advance understanding of an important family of peptides that cause poration of membrane bilayers.
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Affiliation(s)
- K G Schaefer
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, MO 65211, USA
| | - A E Pittman
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, MO 65211, USA
| | - F N Barrera
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - G M King
- Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, MO 65211, USA; Department of Biochemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.
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12
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Schaefer KG, Grau B, Moore N, Mingarro I, King GM, Barrera FN. Controllable membrane remodeling by a modified fragment of the apoptotic protein Bax. Faraday Discuss 2021; 232:114-130. [PMID: 34549736 PMCID: PMC8712456 DOI: 10.1039/d0fd00070a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Intrinsic apoptosis is orchestrated by a group of proteins that mediate the coordinated disruption of mitochondrial membranes. Bax is a multi-domain protein that, upon activation, disrupts the integrity of the mitochondrial outer membrane by forming pores. We strategically introduced glutamic acids into a short sequence of the Bax protein that constitutively creates membrane pores. The resulting BaxE5 peptide efficiently permeabilizes membranes at acidic pH, showing low permeabilization at neutral pH. Atomic force microscopy (AFM) imaging showed that at acidic pH BaxE5 established several membrane remodeling modalities that progressively disturbed the integrity of the lipid bilayer. The AFM data offers vistas on the membrane disruption process, which starts with pore formation and progresses through localized exposure of membrane monolayers leading to stable and small (height ∼ 16 Å) lipid-peptide complexes. The different types of membrane morphology observed in the presence of BaxE5 suggest that the peptide can establish different types of membrane interactions. BaxE5 adopts a rare unstructured conformation when bound to membranes, which might facilitate the dynamic transition between those different states, and then promote membrane digestion.
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Affiliation(s)
- Katherine G Schaefer
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA.
| | - Brayan Grau
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, 37996, USA.
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46100 Burjassot, Spain
| | - Nicolas Moore
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, 37996, USA.
| | - Ismael Mingarro
- Departament de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València, E-46100 Burjassot, Spain
| | - Gavin M King
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA.
- Department of Biochemistry, University of Missouri, Columbia, Missouri, 65211, USA
| | - Francisco N Barrera
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, 37996, USA.
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Kapoor K, Pant S, Tajkhorshid E. Active participation of membrane lipids in inhibition of multidrug transporter P-glycoprotein. Chem Sci 2021; 12:6293-6306. [PMID: 34084427 PMCID: PMC8115088 DOI: 10.1039/d0sc06288j] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Accepted: 03/31/2021] [Indexed: 01/04/2023] Open
Abstract
P-glycoprotein (Pgp) is a major efflux pump in humans, overexpressed in a variety of cancers and associated with the development of multi-drug resistance. Allosteric modulation by various ligands (e.g., transport substrates, inhibitors, and ATP) has been biochemically shown to directly influence structural dynamics, and thereby, the function of Pgp. However, the molecular details of such effects, particularly with respect to the role and involvement of the surrounding lipids, are not well established. Here, we employ all-atom molecular dynamics (MD) simulations to study the conformational landscape of Pgp in the presence of a high-affinity, third-generation inhibitor, tariquidar, in comparison to the nucleotide-free (APO) and the ATP-bound states, in order to characterize the mechanical effects of the inhibitor that might be of relevance to its blocking mechanism of Pgp. Simulations in a multi-component lipid bilayer show a dynamic equilibrium between open(er) and more closed inward-facing (IF) conformations in the APO state, with binding of ATP shifting the equilibrium towards conformations more prone to ATP hydrolysis and subsequent events in the transport cycle. In the presence of the inhibitor bound to the drug-binding pocket within the transmembrane domain (TMD), Pgp samples more open IF conformations, and the nucleotide binding domains (NBDs) become highly dynamic. Interestingly, and reproduced in multiple independent simulations, the inhibitor is observed to facilitate recruitment of lipid molecules into the Pgp lumen through the two proposed drug-entry portals, where the lipid head groups from the cytoplasmic leaflet penetrate into and, in some cases, translocate inside the TMD, while the lipid tails remain extended into the bulk lipid environment. These "wedge" lipids likely enhance the inhibitor-induced conformational restriction of the TMD leading to the differential modulation of coupling pathways observed with the NBDs downstream. We suggest a novel inhibitory mechanism for tariquidar, and potentially for related third-generation Pgp inhibitors, where lipids are seen to enhance the inhibitory role in the catalytic cycle of membrane transporters.
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Affiliation(s)
- Karan Kapoor
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign Urbana IL 61801 USA
| | - Shashank Pant
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign Urbana IL 61801 USA
| | - Emad Tajkhorshid
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign Urbana IL 61801 USA
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14
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Abstract
Drug transporters are integral membrane proteins that play a critical role in drug disposition by affecting absorption, distribution, and excretion. They translocate drugs, as well as endogenous molecules and toxins, across membranes using ATP hydrolysis, or ion/concentration gradients. In general, drug transporters are expressed ubiquitously, but they function in drug disposition by being concentrated in tissues such as the intestine, the kidneys, the liver, and the brain. Based on their primary sequence and their mechanism, transporters can be divided into the ATP-binding cassette (ABC), solute-linked carrier (SLC), and the solute carrier organic anion (SLCO) superfamilies. Many X-ray crystallography and cryo-electron microscopy (cryo-EM) structures have been solved in the ABC and SLC transporter superfamilies or of their bacterial homologs. The structures have provided valuable insight into the structural basis of transport. This chapter will provide particular focus on the promiscuous drug transporters because of their effect on drug disposition and the challenges associated with them.
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Affiliation(s)
- Arthur G Roberts
- Pharmaceutical and Biomedical Sciences Department, University of Georgia, Athens, GA, USA.
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15
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Atkins WM. Mechanisms of promiscuity among drug metabolizing enzymes and drug transporters. FEBS J 2020; 287:1306-1322. [PMID: 31663687 PMCID: PMC7138722 DOI: 10.1111/febs.15116] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 10/04/2019] [Accepted: 10/29/2019] [Indexed: 12/11/2022]
Abstract
Detoxication, or 'drug-metabolizing', enzymes and drug transporters exhibit remarkable substrate promiscuity and catalytic promiscuity. In contrast to substrate-specific enzymes that participate in defined metabolic pathways, individual detoxication enzymes must cope with substrates of vast structural diversity, including previously unencountered environmental toxins. Presumably, evolution selects for a balance of 'adequate' kcat /KM values for a wide range of substrates, rather than optimizing kcat /KM for any individual substrate. However, the structural, energetic, and metabolic properties that achieve this balance, and hence optimize detoxication, are not well understood. Two features of detoxication enzymes that are frequently cited as contributions to promiscuity include the exploitation of highly reactive versatile cofactors, or cosubstrates, and a high degree of flexibility within the protein structure. This review examines these intuitive mechanisms in detail and clarifies the contributions of the classic ligand binding models 'induced fit' (IF) and 'conformational selection' (CS) to substrate promiscuity. The available literature data for drug metabolizing enzymes and transporters suggest that IF is exploited by these promiscuous detoxication enzymes, as it is with substrate-specific enzymes, but the detoxication enzymes uniquely exploit 'IFs' to retain a wide range of substrates at their active sites. In contrast, whereas CS provides no catalytic advantage to substrate-specific enzymes, promiscuous enzymes may uniquely exploit it to recruit a wide range of substrates. The combination of CS and IF, for recruitment and retention of substrates, can potentially optimize the promiscuity of drug metabolizing enzymes and drug transporters.
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Affiliation(s)
- William M. Atkins
- Department of Medicinal ChemistryUniversity of WashingtonSeattleWAUSA
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16
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The effects of anthracycline drugs on the conformational distribution of mouse P-glycoprotein explains their transport rate differences. Biochem Pharmacol 2020; 174:113813. [PMID: 31954717 DOI: 10.1016/j.bcp.2020.113813] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Accepted: 01/13/2020] [Indexed: 01/14/2023]
Abstract
P-glycoprotein (Pgp) is an ATP-dependent efflux transporter and plays a major role in anti-cancer drug resistance by pumping a chemically diverse range of cytotoxic drugs from cancerous tumors. Despite numerous studies with the transporter, the molecular features that drive anti-cancer drug efflux are not well understood. Even subtle differences in the anti-cancer drug molecular structure can lead to dramatic differences in their transport rates. To unmask these structural differences, this study focused on two closely-related anthracycline drugs, daunorubicin (DNR), and doxorubicin (DOX), with mouse Pgp. While only differing by a single hydroxyl functional group, DNR has a 4 to 5-fold higher transport rate than DOX. They both non-competitively inhibited Pgp-mediated ATP hydrolysis below basal levels. The Km of Pgp-mediated ATP hydrolysis extracted from the kinetics curves was lower for DOX than DNR. However, the dissociation constants (KDs) for these drugs determined by fluorescence quenching were virtually identical. Acrylamide quenching of Pgp tryptophan fluorescence to probe the tertiary structure of Pgp suggested that DNR shifts Pgp to a "closed" conformation, while DOX shifts Pgp to an "intermediate" conformation. The effects of these drugs on the Pgp conformational distributions in a lipid bilayer were also examined by atomic force microscopy (AFM). Analysis of AFM images revealed that DNR and DOX cause distinct and significant shifts in the conformational distribution of Pgp. The results were combined to build a conformational distribution model for anthracycline transport by Pgp.
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17
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Kopcho N, Chang G, Komives EA. Dynamics of ABC Transporter P-glycoprotein in Three Conformational States. Sci Rep 2019; 9:15092. [PMID: 31641149 PMCID: PMC6805939 DOI: 10.1038/s41598-019-50578-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 09/10/2019] [Indexed: 12/25/2022] Open
Abstract
We used hydrogen-deuterium exchange mass spectrometry (HDX-MS) to obtain a comprehensive view of transporter dynamics (85.8% sequence coverage) occurring throughout the multidrug efflux transporter P-glycoprotein (P-gp) in three distinct conformational states: predominantly inward-facing apo P-gp, pre-hydrolytic (E552Q/E1197Q) P-gp bound to Mg+2-ATP, and outward-facing P-gp bound to Mg+2-ADP-VO4−3. Nucleotide affinity was measured with bio-layer interferometry (BLI), which yielded kinetics data that fit a two Mg+2-ATP binding-site model. This model has one high affinity site (3.2 ± 0.3 µM) and one low affinity site (209 ± 25 µM). Comparison of deuterium incorporation profiles revealed asymmetry between the changes undergone at the critical interfaces where nucleotide binding domains (NBDs) contact intracellular helices (ICHs). In the pre-hydrolytic state, both interfaces between ICHs and NBDs decreased exchange to similar extents relative to inward-facing P-gp. In the outward-facing state, the ICH-NBD1 interface showed decreased exchange, while the ICH-NBD2 interface showed less of an effect. The extracellular loops (ECLs) showed reduced deuterium uptake in the pre-hydrolytic state, consistent with an occluded conformation. While in the outward-facing state, increased ECL exchange corresponding to EC domain opening was observed. These findings point toward asymmetry between both NBDs, and they suggest that pre-hydrolytic P-gp occupies an occluded conformation.
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Affiliation(s)
- Noah Kopcho
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0378, USA
| | - Geoffrey Chang
- School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Dr, La Jolla, AC, 92093-0754, USA.,Department of Pharmacology, School of Medicine, University of California, San Diego, 9500 Gilman Dr, La Jolla, AC, 92093-0754, USA
| | - Elizabeth A Komives
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0378, USA.
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18
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Crystallization and characterization of small molecular multidrug resistance inhibitor targeting P-glycoprotein, NSC23925 isomers. J Mol Struct 2019. [DOI: 10.1016/j.molstruc.2019.05.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Subramanian N, Schumann-Gillett A, Mark AE, O’Mara ML. Probing the Pharmacological Binding Sites of P-Glycoprotein Using Umbrella Sampling Simulations. J Chem Inf Model 2018; 59:2287-2298. [DOI: 10.1021/acs.jcim.8b00624] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Nandhitha Subramanian
- School of Chemistry and Molecular Biosciences (SCMB), University of Queensland, Brisbane, QLD 4072, Australia
- Research School of Chemistry (RSC), Australian National University, Canberra, ACT 2601, Australia
| | | | - Alan E. Mark
- School of Chemistry and Molecular Biosciences (SCMB), University of Queensland, Brisbane, QLD 4072, Australia
- The Institute for Molecular Biosciences (IMB), University of Queensland, Brisbane, QLD 4072, Australia
| | - Megan L. O’Mara
- School of Chemistry and Molecular Biosciences (SCMB), University of Queensland, Brisbane, QLD 4072, Australia
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