1
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Jiang T, Wan G, Zhang H, Gyawali YP, Underbakke ES, Feng C. Mapping the Intersubunit Interdomain FMN-Heme Interactions in Neuronal Nitric Oxide Synthase by Targeted Quantitative Cross-Linking Mass Spectrometry. Biochemistry 2024; 63:1395-1411. [PMID: 38747545 DOI: 10.1021/acs.biochem.4c00157] [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: 05/29/2024]
Abstract
Nitric oxide synthase (NOS) in mammals is a family of multidomain proteins in which interdomain electron transfer (IET) is controlled by domain-domain interactions. Calmodulin (CaM) binds to the canonical CaM-binding site in the linker region between the FMN and heme domains of NOS and allows tethered FMN domain motions, enabling an intersubunit FMN-heme IET in the output state for NO production. Our previous cross-linking mass spectrometric (XL MS) results demonstrated site-specific protein dynamics in the CaM-responsive regions of rat neuronal NOS (nNOS) reductase construct, a monomeric protein [Jiang et al., Biochemistry, 2023, 62, 2232-2237]. In this work, we have extended our combined approach of XL MS structural mapping and AlphaFold structural prediction to examine the homodimeric nNOS oxygenase/FMN (oxyFMN) construct, an established model of the NOS output state. We employed parallel reaction monitoring (PRM) based quantitative XL MS (qXL MS) to assess the CaM-induced changes in interdomain dynamics and interactions. Intersubunit cross-links were identified by mapping the cross-links onto top AlphaFold structural models, which was complemented by comparing their relative abundances in the cross-linked dimeric and monomeric bands. Furthermore, contrasting the CaM-free and CaM-bound nNOS samples shows that CaM enables the formation of the intersubunit FMN-heme docking complex and that CaM binding induces extensive, allosteric conformational changes across the NOS regions. Moreover, the observed cross-links sites specifically respond to changes in ionic strength. This indicates that interdomain salt bridges are responsible for stabilizing and orienting the output state for efficient FMN-heme IET. Taken together, our targeted qXL MS results have revealed that CaM and ionic strength modulate specific dynamic changes in the CaM/FMN/heme complexes, particularly in the context of intersubunit interdomain FMN-heme interactions.
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Affiliation(s)
- Ting Jiang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Guanghua Wan
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Haikun Zhang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Yadav Prasad Gyawali
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Eric S Underbakke
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011, United States
| | - Changjian Feng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131, United States
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States
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2
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Tumbic GW, Li J, Jiang T, Hossan MY, Feng C, Thielges MC. Interdomain Interactions Modulate the Active Site Dynamics of Human Inducible Nitric Oxide Synthase. J Phys Chem B 2022; 126:6811-6819. [PMID: 36056879 PMCID: PMC10110350 DOI: 10.1021/acs.jpcb.2c04091] [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: 11/28/2022]
Abstract
Nitric oxide synthase (NOS) is a homodimeric flavohemoprotein responsible for catalyzing the oxidation of l-arginine (l-Arg) to citrulline and nitric oxide. Electrons are supplied for the reaction via interdomain electron transfer between an N-terminal heme-containing oxygenase domain and a FMN-containing (sub)domain of a C-terminal reductase domain. Extensive attention has focused on elucidating how conformational dynamics regulate electron transfer between the domains. Here we investigate the impact of the interdomain FMN-heme interaction on the heme active site dynamics of inducible NOS (iNOS). Steady state linear and time-resolved two-dimensional infrared (2D IR) spectroscopy was applied to probe a CO ligand at the heme within the oxygenase domain for full-length and truncated or mutated constructs of human iNOS. Whereas the linear IR spectra of the CO ligand were identical among the constructs, 2D IR spectroscopy revealed variation in the frequency dynamics. The wild-type constructs that can properly form the FMN/oxygenase docked state due to the presence of both the FMN and oxygenase domains showed slower dynamics than the oxygenase domain alone. Introduction of the mutation (E546N) predicted to perturb electrostatic interactions between the domains resulted in measured dynamics intermediate between those for the full-length and individual oxygenase domain, consistent with perturbation to the docked/undocked equilibrium. These results indicate that docking of the FMN domain to the oxygenase domain not only brings the FMN cofactor within electron transfer distance of the heme domain but also modulates the dynamics sensed by the CO ligand within the active site in a way expected to promote efficient electron transfer.
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Affiliation(s)
- Goran W Tumbic
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Jinghui Li
- Department of Pharmaceutical Sciences, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Ting Jiang
- Department of Pharmaceutical Sciences, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Md Yeathad Hossan
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Changjian Feng
- Department of Pharmaceutical Sciences, University of New Mexico, Albuquerque, New Mexico 87131, United States
| | - Megan C Thielges
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
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3
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Stewart AM, Shanmugam M, Kutta RJ, Scrutton NS, Lovett JE, Hay S. Combined Pulsed Electron Double Resonance EPR and Molecular Dynamics Investigations of Calmodulin Suggest Effects of Crowding Agents on Protein Structures. Biochemistry 2022; 61:1735-1742. [PMID: 35979922 PMCID: PMC9454100 DOI: 10.1021/acs.biochem.2c00099] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Calmodulin (CaM) is a highly dynamic Ca2+-binding
protein
that exhibits large conformational changes upon binding Ca2+ and target proteins. Although it is accepted that CaM exists in
an equilibrium of conformational states in the absence of target protein,
the physiological relevance of an elongated helical linker region
in the Ca2+-replete form has been highly debated. In this
study, we use PELDOR (pulsed electron–electron double resonance)
EPR measurements of a doubly spin-labeled CaM variant to assess the
conformational states of CaM in the apo-, Ca2+-bound, and
Ca2+ plus target peptide-bound states. Our findings are
consistent with a three-state conformational model of CaM, showing
a semi-open apo-state, a highly extended Ca2+-replete state,
and a compact target protein-bound state. Molecular dynamics simulations
suggest that the presence of glycerol, and potentially other molecular
crowding agents, has a profound effect on the relative stability of
the different conformational states. Differing experimental conditions
may explain the discrepancies in the literature regarding the observed
conformational state(s) of CaM, and our PELDOR measurements show good
evidence for an extended conformation of Ca2+-replete CaM
similar to the one observed in early X-ray crystal structures.
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Affiliation(s)
- Andrew M Stewart
- The Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames 50011, Iowa, United States.,Manchester Institute of Biotechnology and Department of Chemistry, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K
| | - Muralidharan Shanmugam
- Manchester Institute of Biotechnology and Department of Chemistry, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K
| | - Roger J Kutta
- Manchester Institute of Biotechnology and Department of Chemistry, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.,Institute of Physical and Theoretical Chemistry, University of Regensburg, Regensburg 93040, Germany
| | - Nigel S Scrutton
- Manchester Institute of Biotechnology and Department of Chemistry, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K
| | - Janet E Lovett
- SUPA School of Physics and Astronomy and BSRC, The University of St Andrews, St Andrews KY16 9SS, U.K
| | - Sam Hay
- Manchester Institute of Biotechnology and Department of Chemistry, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K
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4
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Zheng H, Li J, Feng C. Heat shock protein 90 enhances the electron transfer between the FMN and heme cofactors in neuronal nitric oxide synthase. FEBS Lett 2020; 594:2904-2913. [PMID: 32573772 DOI: 10.1002/1873-3468.13870] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Revised: 05/30/2020] [Accepted: 06/04/2020] [Indexed: 11/05/2022]
Abstract
Heat shock protein 90 (Hsp90) is a key regulator of nitric oxide synthase (NOS) in vivo. Despite its functional importance, little is known about the underlying molecular mechanism. Here, purified dimeric human Hsp90α was used to investigate whether (and if so, how) Hsp90 affects the FMN-heme interdomain electron transfer (IET) step in NOS. Hsp90α increases the IET rate for rat neuronal NOS (nNOS) in a dose-saturable manner, and a single charge-neutralization mutation at conserved Hsp90 K585 abolishes the effect. The kinetic results with added Ficoll 70, a crowder, further indicate that Hsp90 enhances the FMN-heme IET through specific association with nNOS. The Hsp90-nNOS docking models provide hints on the putative role of Hsp90 in constraining the available conformational space for the FMN domain motions.
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Affiliation(s)
- Huayu Zheng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA.,Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
| | - Jinghui Li
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA
| | - Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA.,Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
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5
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Astashkin AV, Li J, Zheng H, Feng C. Positional Distributions of the Tethered Modules in Nitric Oxide Synthase: Monte Carlo Calculations and Pulsed EPR Measurements. J Phys Chem A 2019; 123:7075-7086. [PMID: 31310526 DOI: 10.1021/acs.jpca.9b05388] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The nitric oxide synthase (NOS) enzyme consists of multiple domains connected by flexible random coil tethers. In a catalytic cycle, the NOS domains move within the limits determined by the length and flexibility of the interdomain tethers and form docking complexes with each other. This process represents a key component of the electron transport from the flavin adenine dinucleotide/reduced nicotinamide adenine dinucleotide phosphate binding domain to the catalytic heme centers located in the oxygenase domain. Studying the conformational behavior of NOS is therefore imperative for a full understanding of the overall catalytic mechanism. In this work, we have investigated the equilibrium positional distributions of the NOS domains and the bound calmodulin (CaM) by using Monte Carlo calculations of the NOS conformations. As a main experimental reference, we have used the magnetic dipole interaction between a bifunctional spin label attached to T34C/S38C mutant CaM and the NOS heme centers, which was measured by pulsed electron paramagnetic resonance. In general, the calculations of the conformational distributions allow one to determine the range and statistics of positions occupied by the tethered protein domains, assess the crowding effect of the multiple domains on each other, evaluate the accessibility of various potential domain docking sites, and estimate the interaction energies required to achieve target populations of the docked states. In the particular application described here, we have established the specific mechanisms by which the bound CaM facilitates the flavin mononucleotide (FMN)/heme interdomain docking in NOS. We have also shown that the intersubunit FMN/heme domain docking and electron transfer in the homodimeric NOS protein are dictated by the existing structural makeup of the protein. Finally, from comparison of the calculated and experimental docking probabilities, the characteristic stabilization energies for the CaM/heme domain and the FMN domain/heme domain docking complexes have been estimated as -4.5kT and -10.5kT, respectively.
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Affiliation(s)
- Andrei V Astashkin
- Department of Chemistry and Biochemistry , University of Arizona , Tucson , Arizona 85721 , United States
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6
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Molecular mechanism of metabolic NAD(P)H-dependent electron-transfer systems: The role of redox cofactors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1860:233-258. [PMID: 30419202 DOI: 10.1016/j.bbabio.2018.11.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 10/30/2018] [Accepted: 11/07/2018] [Indexed: 12/14/2022]
Abstract
NAD(P)H-dependent electron-transfer (ET) systems require three functional components: a flavin-containing NAD(P)H-dehydrogenase, one-electron carrier and metal-containing redox center. In principle, these ET systems consist of one-, two- and three-components, and the electron flux from pyridine nucleotide cofactors, NADPH or NADH to final electron acceptor follows a linear pathway: NAD(P)H → flavin → one-electron carrier → metal containing redox center. In each step ET is primarily controlled by one- and two-electron midpoint reduction potentials of protein-bound redox cofactors in which the redox-linked conformational changes during the catalytic cycle are required for the domain-domain interactions. These interactions play an effective ET reactions in the multi-component ET systems. The microsomal and mitochondrial cytochrome P450 (cyt P450) ET systems, nitric oxide synthase (NOS) isozymes, cytochrome b5 (cyt b5) ET systems and methionine synthase (MS) ET system include a combination of multi-domain, and their organizations display similarities as well as differences in their components. However, these ET systems are sharing of a similar mechanism. More recent structural information obtained by X-ray and cryo-electron microscopy (cryo-EM) analysis provides more detail for the mechanisms associated with multi-domain ET systems. Therefore, this review summarizes the roles of redox cofactors in the metabolic ET systems on the basis of one-electron redox potentials. In final Section, evolutionary aspects of NAD(P)H-dependent multi-domain ET systems will be discussed.
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7
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Li J, Zheng H, Wang W, Miao Y, Sheng Y, Feng C. Role of an isoform-specific residue at the calmodulin-heme (NO synthase) interface in the FMN - heme electron transfer. FEBS Lett 2018; 592:2425-2431. [PMID: 29904908 DOI: 10.1002/1873-3468.13158] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 05/31/2018] [Accepted: 06/05/2018] [Indexed: 12/18/2022]
Abstract
The interface between calmodulin (CaM) and the NO synthase (NOS) heme domain is the least characterized interprotein interface that the NOS isoforms must traverse through during catalysis. Our previous molecular dynamics simulations predicted a salt bridge between K497 in human inducible NOS (iNOS) heme domain and D118(CaM). Herein, the FMN - heme interdomain electron transfer (IET) rate was found to be notably decreased by charge-reversal mutation, while the IET in the iNOS K497D mutant is significantly restored by the CaM D118K mutation. The results of wild-type protein with added synthetic peptides further demonstrate the critical nature of K497 relative to the rest of the peptide sequence in modulating the IET. These data provide definitive evidence supporting the regulatory role of the isoform-specific K497 residue.
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Affiliation(s)
- Jinghui Li
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA
| | - Huayu Zheng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA.,Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
| | - Wei Wang
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
| | - Yubin Miao
- Department of Radiology, School of Medicine, University of Colorado Denver, Aurora, CO, USA
| | - Yinghong Sheng
- Department of Chemistry & Physics, College of Arts & Sciences, Florida Gulf Coast University, Fort Myers, FL, USA
| | - Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA.,Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
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8
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Arnett DC, Bailey SK, Johnson CK. Exploring the conformations of nitric oxide synthase with fluorescence. Front Biosci (Landmark Ed) 2018; 23:2133-2145. [PMID: 29772550 DOI: 10.2741/4694] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Multi-domain oxidoreductases are a family of enzymes that catalyze oxidation-reduction reactions through a series of electron transfers. Efficient electron transfer requires a sequence of protein conformations that position electron donor and acceptor domains in close proximity to each other so that electron transfer can occur efficiently. An example is mammalian nitric oxide synthase (NOS), which consists of an N-terminal oxygenase domain containing heme and a C-terminal reductase domain containing NADPH/FAD and FMN subdomains. We describe the use of time-resolved and single-molecule fluorescence to detect and characterize the conformations and conformational dynamics of the neuronal and endothelial isoforms of NOS. Fluorescence signals are provided by a fluorescent dye attached to the Ca2+-signaling protein calmodulin (CaM), which regulates NOS activity. Time-resolved fluorescence decays reveal the presence of at least four underlying conformational states that are differentiated by the extent of fluorescence quenching. Single-molecule fluorescence displays transitions between conformational states on the time scales of milliseconds to seconds. This review describes the type of information available by analysis of time-resolved and single-molecule fluorescence experiments.
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Affiliation(s)
- David C Arnett
- Department of Chemistry, Northwestern College, 101 7th Street SW, Orange City, IA 51041
| | - Sheila K Bailey
- Department of Chemistry, University of Kansas, 1251 Wescoe Drive, Lawrence, KS 66045
| | - Carey K Johnson
- Department of Chemistry, University of Kansas, 1251 Wescoe Drive, Lawrence, KS 66045,
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9
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Li J, Zheng H, Feng C. Deciphering mechanism of conformationally controlled electron transfer in nitric oxide synthases. FRONT BIOSCI-LANDMRK 2018; 23:1803-1821. [PMID: 29772530 PMCID: PMC11167721 DOI: 10.2741/4674] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Electron transfer is a fundamental process in life that is very often coupled to catalysis within redox enzymes through a stringent control of protein conformational movements. Mammalian nitric oxide synthase (NOS) proteins are redox flavo-hemoproteins consisting of multiple modular domains. The NOS enzyme is exquisitely regulated in vivo by its partner, the Ca2+ sensing protein calmodulin (CaM), to control production of nitric oxide (NO). The importance of functional domain motion in NOS regulation has been increasingly recognized. The significant size and flexibility of NOS is a tremendous challenge to the mechanistic studies. Herein recent applications of modern biophysical techniques to NOS problems have been critically analyzed. It is important to note that any current biophysical technique alone can only probe partial aspects of the conformational dynamics due to limitations in the technique itself and/or the sample preparations. It is necessary to combine the latest methods to comprehensively quantitate the key conformational aspects (conformational states and distribution, conformational change rates, and domain interacting interfaces) governing the electron transfer. This is to answer long-standing central questions about the NOS isoforms by defining how specific CaM-NOS interactions and regulatory elements underpin the distinct conformational behavior of the NOS isoform, which in turn determine unique electron transfer and NO synthesis properties. This review is not intended as comprehensive, but as a discussion of prospects that promise impact on important questions in the NOS enzymology field.
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Affiliation(s)
- Jinghui Li
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA
| | - Huayu Zheng
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA
| | - Changjian Feng
- University of New Mexico, MSC 09 5360, Albuquerque, NM 87131,
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10
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Astashkin AV, Li J, Zheng H, Miao Y, Feng C. A docked state conformational dynamics model to explain the ionic strength dependence of FMN - heme electron transfer in nitric oxide synthase. J Inorg Biochem 2018; 184:146-155. [PMID: 29751215 DOI: 10.1016/j.jinorgbio.2018.03.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Revised: 03/09/2018] [Accepted: 03/22/2018] [Indexed: 10/17/2022]
Abstract
The FMN-heme interdomain electron transfer (IET) in nitric oxide synthase (NOS) is a key stage of the electron transport chain, which supplies the catalytic heme site(s) with the NADPH-derived electrons. While there is a recognition that this IET depends on both the electron tunneling and the conformational dynamics, the detailed mechanism remains unclear. In this work, the IET kinetics were measured by laser flash photolysis for a bidomain oxygenase/FMN (oxyFMN) construct of human inducible NOS (iNOS) over the ionic strength range from 0.1 to 0.5 M. The forward (heme → FMN, kETf) and backward (FMN → heme, kETb) intrinsic IET rate constants were determined from the analysis of the observed IET rates using the additional information regarding the conformational dynamics obtained from the FMN fluorescence lifetime measurements and theoretical estimates. Both kETf and kETb exhibit a bell-shaped dependence on the ionic strength, I, with the maximum rates corresponding to I ~ 0.2 M. This dependence was explained using a new model, which considers the effect of formation of pairs between the protein surface charged residues and solution ions on the docked state dynamics. The trial simulations of the intrinsic IET rate dependences using this model show that the data can be reproduced using reasonable energetic, structural, and chemical parameters. The suggested model can explain both the monophasic and biphasic ionic strength dependences and can be used to rationalize the interprotein/interdomain electron transfer rates for other types of protein systems where the docked state is sufficiently long-lived.
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Affiliation(s)
- Andrei V Astashkin
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Jinghui Li
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA
| | - Huayu Zheng
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA; Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA
| | - Yubin Miao
- Department of Radiology, School of Medicine, University of Colorado Denver, Aurora, CO 80045, USA
| | - Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA; Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA.
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11
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Hanson QM, Carley JR, Gilbreath TJ, Smith BC, Underbakke ES. Calmodulin-induced Conformational Control and Allostery Underlying Neuronal Nitric Oxide Synthase Activation. J Mol Biol 2018; 430:935-947. [PMID: 29458127 DOI: 10.1016/j.jmb.2018.02.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 02/07/2018] [Accepted: 02/07/2018] [Indexed: 10/18/2022]
Abstract
Nitric oxide synthase (NOS) is the primary generator of nitric oxide signals controlling diverse physiological processes such as neurotransmission and vasodilation. NOS activation is contingent on Ca2+/calmodulin binding at a linker between its oxygenase and reductase domains to induce large conformational changes that orchestrate inter-domain electron transfer. However, the structural dynamics underlying activation of full-length NOS remain ambiguous. Employing hydrogen-deuterium exchange mass spectrometry, we reveal mechanisms underlying neuronal NOS activation by calmodulin and regulation by phosphorylation. We demonstrate that calmodulin binding orders the junction between reductase and oxygenase domains, exposes the FMN subdomain, and elicits a more dynamic oxygenase active site. Furthermore, we demonstrate that phosphorylation partially mimics calmodulin activation to modulate neuronal NOS activity via long-range allostery. Calmodulin binding and phosphorylation ultimately promote a more dynamic holoenzyme while coordinating inter-domain communication and electron transfer.
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Affiliation(s)
- Quinlin M Hanson
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jeffrey R Carley
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Tyler J Gilbreath
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Brian C Smith
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Eric S Underbakke
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
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12
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Hedison TM, Hay S, Scrutton NS. A perspective on conformational control of electron transfer in nitric oxide synthases. Nitric Oxide 2017; 63:61-67. [PMID: 27619338 PMCID: PMC5295631 DOI: 10.1016/j.niox.2016.09.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 09/05/2016] [Accepted: 09/06/2016] [Indexed: 01/20/2023]
Abstract
This perspective reviews single molecule and ensemble fluorescence spectroscopy studies of the three tissue specific nitric oxide synthase (NOS) isoenzymes and the related diflavin oxidoreductase cytochrome P450 reductase. The focus is on the role of protein dynamics and the protein conformational landscape and we discuss how recent fluorescence-based studies have helped in illustrating how the nature of the NOS conformational landscape relates to enzyme turnover and catalysis.
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Affiliation(s)
- Tobias M Hedison
- Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom
| | - Sam Hay
- Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom
| | - Nigel S Scrutton
- Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom.
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13
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Dai Y, Haque MM, Stuehr DJ. Restricting the conformational freedom of the neuronal nitric-oxide synthase flavoprotein domain reveals impact on electron transfer and catalysis. J Biol Chem 2017; 292:6753-6764. [PMID: 28232486 DOI: 10.1074/jbc.m117.777219] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 02/16/2017] [Indexed: 01/02/2023] Open
Abstract
The signaling molecule nitric oxide (NO) is synthesized in animals by structurally related NO synthases (NOSs), which contain NADPH/FAD- and FMN-binding domains. During catalysis, NADPH-derived electrons transfer into FAD and then distribute into the FMN domain for further transfer to internal or external heme groups. Conformational freedom of the FMN domain is thought to be essential for the electron transfer (ET) reactions in NOSs. To directly examine this concept, we utilized a "Cys-lite" neuronal NOS flavoprotein domain and substituted Cys for two residues (Glu-816 and Arg-1229) forming a salt bridge between the NADPH/FAD and FMN domains in the conformationally closed structure to allow cross-domain disulfide bond formation or cross-linking by bismaleimides of various lengths. The disulfide bond cross-link caused a ≥95% loss of cytochrome c reductase activity that was reversible with DTT treatment, whereas graded cross-link lengthening gradually increased activity, thus defining the conformational constraints in the catalytic process. We used spectroscopic and stopped-flow techniques to further investigate how the changes in FMN domain conformational freedom impact the following: (i) the NADPH interaction; (ii) kinetics of electron loading (flavin reduction); (iii) stabilization of open versus closed conformational forms in two different flavin redox states; (iv) reactivity of the reduced FMN domain toward cytochrome c; (v) response to calmodulin binding; and (vi) the rates of interflavin ET and the FMN domain conformational dynamics. Together, our findings help explain how the spatial and temporal behaviors of the FMN domain impact catalysis by the NOS flavoprotein domain and how these behaviors are governed to enable electron flow through the enzyme.
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Affiliation(s)
- Yue Dai
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 and.,the Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
| | - Mohammad Mahfuzul Haque
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 and
| | - Dennis J Stuehr
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 and
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14
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Lipstein N, Göth M, Piotrowski C, Pagel K, Sinz A, Jahn O. Presynaptic Calmodulin targets: lessons from structural proteomics. Expert Rev Proteomics 2017; 14:223-242. [DOI: 10.1080/14789450.2017.1275966] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Noa Lipstein
- Department of Molecular Neurobiology, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
| | - Melanie Göth
- Institute of Chemistry and Biochemistry, Free University Berlin, Berlin & Fritz Haber Institute of the Max-Planck-Society, Berlin, Germany
| | - Christine Piotrowski
- Department of Pharmaceutical Chemistry & Bioanalytics, Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Kevin Pagel
- Institute of Chemistry and Biochemistry, Free University Berlin, Berlin & Fritz Haber Institute of the Max-Planck-Society, Berlin, Germany
| | - Andrea Sinz
- Department of Pharmaceutical Chemistry & Bioanalytics, Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Olaf Jahn
- Proteomics Group, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
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15
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Chen L, Zheng H, Li W, Li W, Miao Y, Feng C. Role of a Conserved Tyrosine Residue in the FMN-Heme Interdomain Electron Transfer in Inducible Nitric Oxide Synthase. J Phys Chem A 2016; 120:7610-7616. [PMID: 27633182 DOI: 10.1021/acs.jpca.6b08207] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The interdomain electron transfer (IET) between the flavin mononucleotide (FMN) and heme domains is essential in the biosynthesis of nitric oxide (NO) by the NO synthase (NOS) enzymes. A conserved tyrosine residue in the FMN domain (Y631 in human inducible NOS) was proposed to be a key part of the electron transfer pathway in the FMN/heme docked complex model. In the present study, the FMN-heme IET kinetics in the Y631F mutant and wild type of a bidomain oxygenase/FMN construct of human inducible NOS were determined by laser flash photolysis. The rate constant of the Y631F mutant is significantly decreased by ∼75% (compared to the wild type), showing that the tyrosine residue indeed facilitates the FMN-heme IET through the protein medium. The IET rate constant of the wild type protein decreases from 345 to 242 s-1 on going from H2O to 95% D2O, giving a solvent kinetic isotope effect of 1.4. In contrast, no deuterium isotope effect was observed for the Tyr-to-Phe mutant. Moreover, an appreciable change in the wild type iNOS IET rate constant value was observed upon changing pH. These results indicate that the FMN-heme IET is proton coupled, in which the conserved tyrosine residue may play an important role.
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Affiliation(s)
- Li Chen
- College of Pharmacy, University of New Mexico , Albuquerque, New Mexico 87131, United States
| | - Huayu Zheng
- College of Pharmacy, University of New Mexico , Albuquerque, New Mexico 87131, United States.,Department of Chemistry and Chemical Biology, University of New Mexico , Albuquerque, New Mexico 87131, United States
| | - Wenbing Li
- College of Pharmacy, University of New Mexico , Albuquerque, New Mexico 87131, United States
| | - Wei Li
- College of Pharmacy, University of New Mexico , Albuquerque, New Mexico 87131, United States
| | - Yubin Miao
- Radiology, University of Colorado Denver , Denver, Colorado 80045, United States
| | - Changjian Feng
- College of Pharmacy, University of New Mexico , Albuquerque, New Mexico 87131, United States.,Department of Chemistry and Chemical Biology, University of New Mexico , Albuquerque, New Mexico 87131, United States
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16
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Hedison TM, Leferink NGH, Hay S, Scrutton NS. Correlating Calmodulin Landscapes with Chemical Catalysis in Neuronal Nitric Oxide Synthase using Time-Resolved FRET and a 5-Deazaflavin Thermodynamic Trap. ACS Catal 2016; 6:5170-5180. [PMID: 27563493 PMCID: PMC4993522 DOI: 10.1021/acscatal.6b01280] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2016] [Revised: 06/23/2016] [Indexed: 11/28/2022]
Abstract
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A major challenge in enzymology is
the need to correlate the dynamic
properties of enzymes with, and understand the impact on, their catalytic
cycles. This is especially the case with large, multicenter enzymes
such as the nitric oxide synthases (NOSs), where the importance of
dynamics has been inferred from a variety of structural, single-molecule,
and ensemble spectroscopic approaches but where motions have not been
correlated experimentally with mechanistic steps in the reaction cycle.
Here we take such an approach. Using time-resolved spectroscopy employing
absorbance and Förster resonance energy transfer (FRET) and
exploiting the properties of a flavin analogue (5-deazaflavin mononucleotide
(5-dFMN)) and isotopically labeled nicotinamide coenzymes, we correlate
the timing of CaM structural changes when bound to neuronal nitric
oxide synthase (nNOS) with the nNOS catalytic cycle. We show that
remodeling of CaM occurs early in the electron transfer sequence (FAD
reduction), not at later points in the reaction cycle (e.g., FMN reduction).
Conformational changes are tightly correlated with FAD reduction kinetics
and reflect a transient “opening” and then “closure”
of the bound CaM molecule. We infer that displacement of the C-terminal
tail on binding NADPH and subsequent FAD reduction are the likely
triggers of conformational change. By combining the use of cofactor/coenzyme
analogues and time-resolved FRET/absorbance spectrophotometry, we
show how the reaction cycles of complex enzymes can be simplified,
enabling a detailed study of the relationship between protein dynamics
and reaction cycle chemistry—an approach that can also be used
with other complex multicenter enzymes.
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Affiliation(s)
- Tobias M. Hedison
- Manchester Synthetic Biology
Research Centre for Fine and Speciality Chemicals (SYNBIOCHEM), Manchester
Institute of Biotechnology, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - Nicole G. H. Leferink
- Manchester Synthetic Biology
Research Centre for Fine and Speciality Chemicals (SYNBIOCHEM), Manchester
Institute of Biotechnology, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - Sam Hay
- Manchester Synthetic Biology
Research Centre for Fine and Speciality Chemicals (SYNBIOCHEM), Manchester
Institute of Biotechnology, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - Nigel S. Scrutton
- Manchester Synthetic Biology
Research Centre for Fine and Speciality Chemicals (SYNBIOCHEM), Manchester
Institute of Biotechnology, The University of Manchester, Manchester M1 7DN, United Kingdom
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17
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Meyer A, Schiemann O. PELDOR and RIDME Measurements on a High-Spin Manganese(II) Bisnitroxide Model Complex. J Phys Chem A 2016; 120:3463-72. [DOI: 10.1021/acs.jpca.6b00716] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Andreas Meyer
- Institute of Physical and
Theoretical Chemistry, University of Bonn, Wegelerstr. 12, Bonn, Germany
| | - Olav Schiemann
- Institute of Physical and
Theoretical Chemistry, University of Bonn, Wegelerstr. 12, Bonn, Germany
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18
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Astashkin AV, Feng C. Solving Kinetic Equations for the Laser Flash Photolysis Experiment on Nitric Oxide Synthases: Effect of Conformational Dynamics on the Interdomain Electron Transfer. J Phys Chem A 2015; 119:11066-75. [PMID: 26477677 DOI: 10.1021/acs.jpca.5b08414] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The production of nitric oxide by the nitric oxide synthase (NOS) enzyme depends on the interdomain electron transfer (IET) between the flavin mononucleotide (FMN) and heme domains. Although the rate of this IET has been measured by laser flash photolysis (LFP) for various NOS proteins, no rigorous analysis of the relevant kinetic equations was performed so far. In this work, we provide an analytical solution of the kinetic equations underlying the LFP approach. The derived expressions reveal that the bulk IET rate is significantly affected by the conformational dynamics that determines the formation and dissociation rates of the docking complex between the FMN and heme domains. We show that in order to informatively study the electron transfer across the NOS enzyme, LFP should be used in combination with other spectroscopic methods that could directly probe the docking equilibrium and the conformational change rate constants. The implications of the obtained analytical expressions for the interpretation of the LFP results from various native and modified NOS proteins are discussed. The mathematical formulas derived in this work should also be applicable for interpreting the IET kinetics in other modular redox enzymes.
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Affiliation(s)
- Andrei V Astashkin
- Department of Chemistry and Biochemistry, University of Arizona , Tucson, Arizona 85721, United States
| | - Changjian Feng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico , Albuquerque, New Mexico 87131, United States
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19
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Hollingsworth SA, Holden JK, Li H, Poulos TL. Elucidating nitric oxide synthase domain interactions by molecular dynamics. Protein Sci 2015; 25:374-82. [PMID: 26448477 PMCID: PMC4815339 DOI: 10.1002/pro.2824] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Revised: 09/25/2015] [Accepted: 10/04/2015] [Indexed: 12/19/2022]
Abstract
Nitric oxide synthase (NOS) is a multidomain enzyme that catalyzes the production of nitric oxide (NO) by oxidizing L-Arg to NO and L-citrulline. NO production requires multiple interdomain electron transfer steps between the flavin mononucleotide (FMN) and heme domain. Specifically, NADPH-derived electrons are transferred to the heme-containing oxygenase domain via the flavin adenine dinucleotide (FAD) and FMN containing reductase domains. While crystal structures are available for both the reductase and oxygenase domains of NOS, to date there is no atomic level structural information on domain interactions required for the final FMN-to-heme electron transfer step. Here, we evaluate a model of this final electron transfer step for the heme-FMN-calmodulin NOS complex based on the recent biophysical studies using a 105-ns molecular dynamics trajectory. The resulting equilibrated complex structure is very stable and provides a detailed prediction of interdomain contacts required for stabilizing the NOS output state. The resulting equilibrated complex model agrees well with previous experimental work and provides a detailed working model of the final NOS electron transfer step required for NO biosynthesis.
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Affiliation(s)
- Scott A Hollingsworth
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, 92697.,Department of Chemistry, University of California, Irvine, California, 92697.,Department of Pharmaceutical Sciences, University of California, Irvine, California, 92697
| | - Jeffrey K Holden
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, 92697.,Department of Chemistry, University of California, Irvine, California, 92697.,Department of Pharmaceutical Sciences, University of California, Irvine, California, 92697
| | - Huiying Li
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, 92697.,Department of Chemistry, University of California, Irvine, California, 92697.,Department of Pharmaceutical Sciences, University of California, Irvine, California, 92697
| | - Thomas L Poulos
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, 92697.,Department of Chemistry, University of California, Irvine, California, 92697.,Department of Pharmaceutical Sciences, University of California, Irvine, California, 92697
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20
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Sheng Y, Zhong L, Guo D, Lau G, Feng C. Insight into structural rearrangements and interdomain interactions related to electron transfer between flavin mononucleotide and heme in nitric oxide synthase: A molecular dynamics study. J Inorg Biochem 2015; 153:186-196. [PMID: 26277414 DOI: 10.1016/j.jinorgbio.2015.08.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Revised: 06/29/2015] [Accepted: 08/05/2015] [Indexed: 10/23/2022]
Abstract
Calmodulin (CaM) binding to nitric oxide synthase (NOS) enables a conformational change, in which the FMN domain shuttles between the FAD and heme domains to deliver electrons to the active site heme center. A clear understanding of this large conformational change is critical, since this step is the rate-limiting in NOS catalysis. Herein molecular dynamics simulations were conducted on a model of an oxygenase/FMN (oxyFMN) construct of human inducible NOS (iNOS). This is to investigate the structural rearrangements and the domain interactions related to the FMN-heme interdomain electron transfer (IET). We carried out simulations on the iNOS oxyFMN·CaM complex models in [Fe(III)][FMNH(-)] and [Fe(II)][FMNH] oxidation states, the pre- and post-IET states. The comparison of the dynamics and conformations of the iNOS construct at the two oxidation states has allowed us to identify key factors related to facilitating the FMN-heme IET process. The computational results demonstrated, for the first time, that the conformational change is redox-dependent. Predictions of the key interacting sites in optimal interdomain FMN/heme docking are well supported by experimental data in the literature. An intra-subunit pivot region is predicted to modulate the FMN domain motion and correlate with existence of a bottleneck in the conformational sampling that leads to the electron transfer-competent state. Interactions of the residues identified in this work are proposed to ensure that the FMN domain moves with appropriate degrees of freedom and docks to proper positions at the heme domain, resulting in efficient IET and nitric oxide production.
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Affiliation(s)
- Yinghong Sheng
- Department of Chemistry & Physics, College of Arts & Sciences, Florida Gulf Coast University, 10501 FGCU Blvd. S., Fort Myers, FL 33965, USA.
| | - Linghao Zhong
- Pennsylvania State University at Mont Alto, 1 Campus Drive, Mont Alto, PA 17237, USA
| | - Dahai Guo
- Department of Bioengineering and Software Engineering, U.A. Whitaker College of Engineering, Florida Gulf Coast University, 10501 FGCU Blvd. S., Fort Myers, FL 33965, USA
| | - Gavin Lau
- Department of Chemistry & Physics, College of Arts & Sciences, Florida Gulf Coast University, 10501 FGCU Blvd. S., Fort Myers, FL 33965, USA
| | - Changjian Feng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA.
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21
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Arnett DC, Persechini A, Tran QK, Black DJ, Johnson CK. Fluorescence quenching studies of structure and dynamics in calmodulin-eNOS complexes. FEBS Lett 2015; 589:1173-8. [PMID: 25871521 DOI: 10.1016/j.febslet.2015.03.035] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 03/17/2015] [Accepted: 03/31/2015] [Indexed: 10/23/2022]
Abstract
Activation of endothelial nitric oxide synthase (eNOS) by calmodulin (CaM) facilitates formation of a sequence of conformational states that is not well understood. Fluorescence decays of fluorescently labeled CaM bound to eNOS reveal four distinct conformational states and single-molecule fluorescence trajectories show multiple fluorescence states with transitions between states occurring on time scales of milliseconds to seconds. A model is proposed relating fluorescence quenching states to enzyme conformations. Specifically, we propose that the most highly quenched state corresponds to CaM docked to an oxygenase domain of the enzyme. In single-molecule trajectories, this state occurs with time lags consistent with the oxygenase activity of the enzyme.
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Affiliation(s)
- David C Arnett
- Department of Chemistry, University of Kansas, Lawrence, KS 66045, USA; Department of Chemistry, Northwestern College, Orange City, IA 51041, USA
| | - Anthony Persechini
- Division of Molecular Biology and Biochemistry and Division of Cell Biology and Biophysics, University of Missouri at Kansas City, Kansas City, MO 64410, USA
| | - Quang-Kim Tran
- Division of Molecular Biology and Biochemistry and Division of Cell Biology and Biophysics, University of Missouri at Kansas City, Kansas City, MO 64410, USA
| | - D J Black
- Division of Molecular Biology and Biochemistry and Division of Cell Biology and Biophysics, University of Missouri at Kansas City, Kansas City, MO 64410, USA
| | - Carey K Johnson
- Department of Chemistry, University of Kansas, Lawrence, KS 66045, USA.
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22
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23
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Leferink NGH, Hay S, Rigby SEJ, Scrutton NS. Towards the free energy landscape for catalysis in mammalian nitric oxide synthases. FEBS J 2014; 282:3016-29. [PMID: 25491181 DOI: 10.1111/febs.13171] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2014] [Revised: 12/05/2014] [Accepted: 12/05/2014] [Indexed: 01/30/2023]
Abstract
The general requirement for conformational sampling in biological electron transfer reactions catalysed by multi-domain redox systems has been emphasized in recent years. Crucially, we lack insight into the extent of the conformational space explored and the nature of the energy landscapes associated with these reactions. The nitric oxide synthases (NOS) produce the signalling molecule NO through a series of complex electron transfer reactions. There is accumulating evidence that protein domain dynamics and calmodulin binding are implicated in regulating electron flow from NADPH, through the FAD and FMN cofactors, to the haem oxygenase domain, where NO is generated. Simple models based on static crystal structures of the isolated reductase domain have suggested a role for large-scale motions of the FMN-binding domain in shuttling electrons from the reductase domain to the oxygenase domain. However, detailed insight into the higher-order domain architecture and dynamic structural transitions in NOS enzymes during enzyme turnover is lacking. In this review, we discuss the recent advances made towards mapping the catalytic free energy landscapes of NOS enzymes through integration of both structural techniques (e.g. cryo-electron microscopy) and biophysical techniques (e.g. pulsed-electron paramagnetic resonance). The general picture that emerges from these experiments is that NOS enzymes exist in an equilibrium of conformations, comprising a 'rugged' or 'frustrated' energy landscape, with a key regulatory role for calmodulin in driving vectorial electron transfer by altering the conformational equilibrium. A detailed understanding of these landscapes may provide new opportunities for discovery of isoform-specific inhibitors that bind at the dynamic interfaces of these multi-dimensional energy landscapes.
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Affiliation(s)
- Nicole G H Leferink
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
| | - Sam Hay
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
| | - Stephen E J Rigby
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
| | - Nigel S Scrutton
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
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