1
|
Xu G, Wang Q, Ma J. OPUS-Mut: Studying the Effect of Protein Mutation through Side-Chain Modeling. J Chem Theory Comput 2023; 19:1629-1640. [PMID: 36813264 PMCID: PMC10018731 DOI: 10.1021/acs.jctc.2c00847] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Predicting the effect of protein mutation is crucial in many applications such as protein design, protein evolution, and genetic disease analysis. Structurally, mutation is basically the replacement of the side chain of a particular residue. Therefore, accurate side-chain modeling is useful in studying the effect of mutation. Here, we propose a computational method, namely, OPUS-Mut, which significantly outperforms other backbone-dependent side-chain modeling methods including our previous method OPUS-Rota4. We evaluate OPUS-Mut by four case studies on Myoglobin, p53, HIV-1 protease, and T4 lysozyme. The results show that the predicted structures of side chains of different mutants are consistent well with their experimentally determined results. In addition, when the residues with significant structural shifts upon the mutation are considered, it is found that the extent of the predicted structural shift of these affected residues can be correlated reasonably well with the functional changes of the mutant measured by experiments. OPUS-Mut can also help one to identify the harmful and benign mutations and thus may guide the construction of a protein with relatively low sequence homology but with a similar structure.
Collapse
Affiliation(s)
- Gang Xu
- Multiscale Research Institute of Complex Systems, Fudan University, Shanghai 200433, China.,Zhangjiang Fudan International Innovation Center, Fudan University, Shanghai 201210, China.,Shanghai AI Laboratory, Shanghai 200030, China
| | - Qinghua Wang
- Center for Biomolecular Innovation, Harcam Biomedicines, Shanghai 200131, China
| | - Jianpeng Ma
- Multiscale Research Institute of Complex Systems, Fudan University, Shanghai 200433, China.,Zhangjiang Fudan International Innovation Center, Fudan University, Shanghai 201210, China.,Shanghai AI Laboratory, Shanghai 200030, China
| |
Collapse
|
2
|
Freindorf M, Delgado AAA, Kraka E. CO bonding in hexa‐ and pentacoordinate carboxy‐neuroglobin: A quantum mechanics/molecular mechanics and local vibrational mode study. J Comput Chem 2022. [DOI: 10.1002/jcc.26973] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Marek Freindorf
- Department of Chemistry Southern Methodist University Dallas Texas USA
| | | | - Elfi Kraka
- Department of Chemistry Southern Methodist University Dallas Texas USA
| |
Collapse
|
3
|
Olson JS. Kinetic mechanisms for O 2 binding to myoglobins and hemoglobins. Mol Aspects Med 2021; 84:101024. [PMID: 34544605 DOI: 10.1016/j.mam.2021.101024] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 09/06/2021] [Accepted: 09/12/2021] [Indexed: 11/29/2022]
Abstract
Antonini and Brunori's 1971 book "Hemoglobin and Myoglobin in Their Reactions with Ligands" was a truly remarkable publication that summarized almost 100 years of research on O2 binding to these globins. Over the ensuing 50 years, ultra-fast laser photolysis techniques, high-resolution and time resolved X-ray crystallography, molecular dynamics simulations, and libraries of recombinant myoglobin (Mb) and hemoglobin (Hb) variants have provided structural interpretations of O2 binding to these proteins. The resultant mechanisms provide quantitative descriptions of the stereochemical factors that govern overall affinity, including proximal and distal steric restrictions that affect iron reactivity and favorable positive electrostatic interactions that preferentially stabilize bound O2. The pathway for O2 uptake and release by Mb and subunits of Hb has been mapped by screening libraries of site-directed mutants in laser photolysis experiments. O2 enters mammalian Mb and the α and β subunits of human HbA through a channel created by upward and outward rotation of the distal His at the E7 helical position, is non-covalently captured in the interior of the distal cavity, and then internally forms a bond with the heme Fe(II) atom. O2 dissociation is governed by disruption of hydrogen bonding interactions with His (E7), breakage of the Fe(II)-O2 bond, and then competition between rebinding and escape through the E7-gate. The structural features that govern the rates of both the individual steps and overall reactions have been determined and provide the framework for: (1) defining the physiological functions of specific globins and their evolution; (2) understanding the clinical features of hemoglobinopathies; and (3) designing safer and more efficient acellular hemoglobin-based oxygen carriers (HBOCs) for transfusion therapy, organ preservation, and other commercially relevant O2 transport and storage processes.
Collapse
Affiliation(s)
- John S Olson
- Department of Biosciences, Rice University, Houston, TX, 77005, USA.
| |
Collapse
|
4
|
Thompson MK, Shay MR, de Serrano V, Dumarieh R, Ghiladi RA, Franzen S. A new inhibition mechanism in the multifunctional catalytic hemoglobin dehaloperoxidase as revealed by the DHP A(V59W) mutant: A spectroscopic and crystallographic study. J PORPHYR PHTHALOCYA 2021. [DOI: 10.1142/s1088424621500826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
As multifunctional catalytic hemoglobins, dehaloperoxidase isoenzymes A and B (DHP A and B) are among the most versatile hemoproteins in terms of activities displayed. The ability of DHP to bind over twenty different substrates in the distal pocket might appear to resemble the promiscuousness of monooxygenase enzymes, yet there are identifiable substrate-specific interactions that can steer the type of oxidation (O-atom vs. electron transfer) that occurs inside the DHP distal pocket. Here, we have investigated the DHP A(V59W) mutant in order to probe the limits of conformational flexibility in the distal pocket as it relates to the genesis of this substrate-dependent activity differentiation. The X-ray crystal structure of the metaquo DHP A(V59W) mutant (PDB 3K3U) and the V59W mutant in complex with fluoride [denoted as DHP A(V59W-F)] (PDB 7MNH) show significant mobility of the tryptophan in the distal pocket, with two parallel conformations having W59-N[Formula: see text] H-bonded to a heme-bound ligand (H2O or F[Formula: see text], and another conformation [observed only in DHP A(V59W-F)] that brings W59 sufficiently close to the heme as to preclude axial ligand binding. UV-vis and resonance Raman spectroscopic studies show that DHP A(V59W) is 5-coordinate high spin (5cHS) at pH 5 and 6-coordinate high spin (6cHS) at pH 7, whereas DHP A(V59W-F) is 6cHS from pH 5 to 7. Enzyme assays confirm robust peroxidase activity at pH 5, but complete loss of activity at pH 7. We find no evidence that tryptophan plays a role in the oxidation mechanism ([Formula: see text]. radical formation). Instead, the data reveal a new mechanism of DHP inhibition, namely a shift towards a non-reactive form by OH[Formula: see text] ligation to the heme-Fe that is strongly stabilized (presumably through H-bonding interactions) by the presence of W59 in the distal cavity.
Collapse
Affiliation(s)
- Matthew K. Thompson
- Department of Chemistry & Biochemistry, University of Alabama, 250 Hackberry Lane, Tuscaloosa, AL 35487, USA
| | - Madeline R. Shay
- Department of Chemistry & Biochemistry, University of Alabama, 250 Hackberry Lane, Tuscaloosa, AL 35487, USA
| | - Vesna de Serrano
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Rania Dumarieh
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Reza A. Ghiladi
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Stefan Franzen
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| |
Collapse
|
5
|
Freindorf M, Kraka E. Critical assessment of the FeC and CO bond strength in carboxymyoglobin: a QM/MM local vibrational mode study. J Mol Model 2020; 26:281. [DOI: 10.1007/s00894-020-04519-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 08/26/2020] [Indexed: 12/15/2022]
|
6
|
Diamantis P, Hage KE, Meuwly M. Effect of Single-Point Mutations on Nitric Oxide Rebinding and the Thermodynamic Stability of Myoglobin. J Phys Chem B 2019; 123:1961-1972. [PMID: 30724565 DOI: 10.1021/acs.jpcb.8b11454] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effect of single amino acid mutations on the rebinding dynamics of nitrogen monoxide (NO) to myoglobin is investigated using reactive molecular dynamics simulations. In particular, mutations of residues surrounding the heme-active site (Leu29, His64, Val68) were considered. Consistent with experiments, all mutations studied here have a significant effect on the kinetics of the NO-rebinding process, which consists of a rapid (several 10 ps) and a slow (100s of ps) time scale. For all modifications considered, the time scales and rebinding fractions agree to within a few percents with results from experiments by adjusting one single, physically meaningful, conformationally averaged quantity: the asymptotic energy separation between the NO-bound (2A) and photodissociated (4A) states. It is furthermore shown that the thermodynamic stability of wild-type versus mutant Mb for the ligand-free and ligand-bound variants of the protein can be described by the same computational model. Therefore, ligand kinetics and thermodynamics are related in a direct fashion akin to Φ-value analysis, which establishes a relationship between protein folding rates and thermal stability of proteins.
Collapse
Affiliation(s)
- Polydefkis Diamantis
- Department of Chemistry , University of Basel , Klingelbergstrasse 80 , 4056 Basel , Switzerland
| | - Krystel El Hage
- Department of Chemistry , University of Basel , Klingelbergstrasse 80 , 4056 Basel , Switzerland
| | - Markus Meuwly
- Department of Chemistry , University of Basel , Klingelbergstrasse 80 , 4056 Basel , Switzerland.,Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| |
Collapse
|
7
|
Horn M, Nienhaus K, Nienhaus GU. Kinetic Study of Ligand Binding and Conformational Changes in Inducible Nitric Oxide Synthase. J Phys Chem B 2018; 122:11048-11057. [PMID: 29965771 DOI: 10.1021/acs.jpcb.8b05137] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Nitric oxide synthases (NOSs) are heme enzymes that generate highly reactive nitric oxide from l-arginine (l-Arg) in a complex mechanism that is still only partially understood. We have studied carbon monoxide (CO) binding to the oxygenase domain of murine inducible NOS (iNOS) by using flash photolysis. The P420 and P450 forms of the enzyme, assigned to a protonated and unprotonated proximal cysteine, through which the heme is anchored to the protein, show markedly different CO rebinding properties. The data suggest that P420 has a widely open distal pocket that admits water. CO rebinding to the P450 form strongly depends on the presence of the substrate l-Arg, the intermediate Nω-hydroxy-l-arginine, and the cofactor tetrahydrobiopterin. After adding these small molecules to the enzyme solution, the CO kinetics change slowly over the hours. This process can be described as a relaxation from a fast rebinding, metastable species to a slowly rebinding, thermodynamically stable species, which we associate with the enzymatically active form. Our results allow us to determine kinetic parameters of l-Arg binding to the ferrous deoxy iNOS protein for the first time and also provide clues regarding the nature of structural differences between the two interconverting species.
Collapse
Affiliation(s)
- Michael Horn
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1 , D-76131 Karlsruhe , Germany
| | - Karin Nienhaus
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1 , D-76131 Karlsruhe , Germany
| | - G Ulrich Nienhaus
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1 , D-76131 Karlsruhe , Germany.,Institute of Nanotechnology (INT) and Institute of Toxicology and Genetics (ITG), Karlsruhe Institute of Technology (KIT) , D-76344 Eggenstein-Leopoldshafen , Germany.,Department of Physics , University of Illinois at Urbana-Champaign , 1110 West Green Street , Urbana , Illinois 61801 , United States
| |
Collapse
|
8
|
Wang XW, Zhang JZH, He X. Ab initio Quantum Mechanics/Molecular Mechanics Molecular Dynamics Simulation of CO in the Heme Distal Pocket of Myoglobin. CHINESE J CHEM PHYS 2017. [DOI: 10.1063/1674-0068/30/cjcp1709169] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Xian-wei Wang
- College of Science, Zhejiang University of Technology, Hangzhou 310023, China
- College of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
- Zhejiang Provincial Collaborative Innovation Center of High-end Laser Manufacturing Equipment, Hangzhou 310014, China
| | - John Z. H. Zhang
- College of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
- NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai 200062, China
- Department of Chemistry, New York University, New York 10003, USA
| | - Xiao He
- College of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
- NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai 200062, China
| |
Collapse
|
9
|
Mohammadi M, Vashisth H. Pathways and Thermodynamics of Oxygen Diffusion in [FeFe]-Hydrogenase. J Phys Chem B 2017; 121:10007-10017. [DOI: 10.1021/acs.jpcb.7b06489] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Mohammadjavad Mohammadi
- Department of Chemical Engineering, University of New Hampshire, Durham 03824, New Hampshire, United States
| | - Harish Vashisth
- Department of Chemical Engineering, University of New Hampshire, Durham 03824, New Hampshire, United States
| |
Collapse
|
10
|
Nienhaus K, Nickel E, Nienhaus GU. Substrate binding in human indoleamine 2,3-dioxygenase 1: A spectroscopic analysis. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:453-463. [DOI: 10.1016/j.bbapap.2017.02.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Revised: 01/22/2017] [Accepted: 02/07/2017] [Indexed: 11/27/2022]
|
11
|
Sharma S, Kumar A, Kundu S, Bandyopadhyay P. Molecular dynamics simulations indicate that tyrosineB10 limits motions of distal histidine to regulate CO binding in soybean leghemoglobin. Proteins 2015; 83:1836-48. [PMID: 26211916 DOI: 10.1002/prot.24867] [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: 08/16/2014] [Revised: 07/01/2015] [Accepted: 07/21/2015] [Indexed: 11/09/2022]
Abstract
Myoglobin (Mb) uses strong electrostatic interaction in its distal heme pocket to regulate ligand binding. The mechanism of regulation of ligand binding in soybean leghemoglobin a (Lba) has been enigmatic and more so due to the absence of gaseous ligand bound atomic resolution three-dimensional structure of the plant globin. While the 20-fold higher oxygen affinity of Lba compared with Mb is required for its dual physiological function, the mechanism by which this high affinity is achieved is only emerging. Extensive mutational analysis combined with kinetic and CO-FT-IR spectroscopic investigation led to the hypothesis that Lba depended on weakened electrostatic interaction between distal HisE7 and bound ligand achieved by invoking B10Tyr, which itself hydrogen bonds with HisE7 thus restricting it in a single conformation detrimental to Mb-like strong electrostatic interaction. Such theory has been re-assessed here using CO-Lba in silico model and molecular dynamics simulation. The investigation supports the presence of at least two major conformations of HisE7 in Lba brought about by imidazole ring flip, one of which makes hydrogen bonds effectively with B10Tyr affecting the former's ability to stabilize bound ligand, while the other does not. However, HisE7 in Lba has limited conformational freedom unlike high frequency of imidazole ring flips observed in Mb and in TyrB10Leu mutant of Lba. Thus, it appears that TyrB10 limits the conformational freedom of distal His in Lba, tuning down ligand dissociation rate constant by reducing the strength of hydrogen bonding to bound ligand, which the freedom of distal His of Mb allows.
Collapse
Affiliation(s)
- Smriti Sharma
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Amit Kumar
- Department of Biochemistry, University of Delhi South Campus, New Delhi, 110021, India
| | - Suman Kundu
- Department of Biochemistry, University of Delhi South Campus, New Delhi, 110021, India
| | - Pradipta Bandyopadhyay
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| |
Collapse
|
12
|
Ligand-induced protein responses and mechanical signal propagation described by linear response theories. Biophys J 2015; 107:1415-25. [PMID: 25229149 DOI: 10.1016/j.bpj.2014.07.049] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 06/18/2014] [Accepted: 07/15/2014] [Indexed: 02/04/2023] Open
Abstract
In this study, a general linear response theory (LRT) is formulated to describe time-dependent and -independent protein conformational changes upon CO binding with myoglobin. Using the theory, we are able to monitor protein relaxation in two stages. The slower relaxation is found to occur from 4.4 to 81.2 picoseconds and the time constants characterized for a couple of aromatic residues agree with those observed by UV Resonance Raman (UVRR) spectrometry and time resolved x-ray crystallography. The faster "early responses", triggered as early as 400 femtoseconds, can be best described by the theory when impulse forces are used. The newly formulated theory describes the mechanical propagation following ligand-binding as a function of time, space and types of the perturbation forces. The "disseminators", defined as the residues that propagate signals throughout the molecule the fastest among all the residues in protein when perturbed, are found evolutionarily conserved and the mutations of which have been shown to largely change the CO rebinding kinetics in myoglobin.
Collapse
|
13
|
Horn M, Nienhaus K, Nienhaus GU. Fourier transform infrared spectroscopy study of ligand photodissociation and migration in inducible nitric oxide synthase. F1000Res 2014; 3:290. [PMID: 25653844 DOI: 10.12688/f1000research.5836.1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/27/2014] [Indexed: 03/23/2024] Open
Abstract
Inducible nitric oxide synthase (iNOS) is a homodimeric heme enzyme that catalyzes the formation of nitric oxide (NO) from dioxygen and L-arginine (L-Arg) in a two-step process. The produced NO can either diffuse out of the heme pocket into the surroundings or it can rebind to the heme iron and inhibit enzyme action. Here we have employed Fourier transform infrared (FTIR) photolysis difference spectroscopy at cryogenic temperatures, using the carbon monoxide (CO) and NO stretching bands as local probes of the active site of iNOS. Characteristic changes were observed in the spectra of the heme-bound ligands upon binding of the cofactors. Unlike photolyzed CO, which becomes trapped in well-defined orientations, as indicated by sharp photoproduct bands, photoproduct bands of NO photodissociated from the ferric heme iron were not visible, indicating that NO does not reside in the protein interior in a well-defined location or orientation. This may be favorable for NO release from the enzyme during catalysis because it reduces self-inhibition. Moreover, we used temperature derivative spectroscopy (TDS) with FTIR monitoring to explore the dynamics of NO and carbon monoxide (CO) inside iNOS after photodissociation at cryogenic temperatures. Only a single kinetic photoproduct state was revealed, but no secondary docking sites as in hemoglobins. Interestingly, we observed that intense illumination of six-coordinate ferrous iNOS oxy-NO ruptures the bond between the heme iron and the proximal thiolate to yield five-coordinate ferric iNOS oxy-NO, demonstrating the strong trans effect of the heme-bound NO.
Collapse
Affiliation(s)
- Michael Horn
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics, Karlsruhe, D-76131, Germany
| | - Karin Nienhaus
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics, Karlsruhe, D-76131, Germany
| | - Gerd Ulrich Nienhaus
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics, Karlsruhe, D-76131, Germany ; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| |
Collapse
|
14
|
Horn M, Nienhaus K, Nienhaus GU. Fourier transform infrared spectroscopy study of ligand photodissociation and migration in inducible nitric oxide synthase. F1000Res 2014; 3:290. [PMID: 25653844 PMCID: PMC4304226 DOI: 10.12688/f1000research.5836.2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 12/11/2014] [Indexed: 11/20/2022] Open
Abstract
Inducible nitric oxide synthase (iNOS) is a homodimeric heme enzyme that catalyzes the formation of nitric oxide (NO) from dioxygen and L-arginine (L-Arg) in a two-step process. The produced NO can either diffuse out of the heme pocket into the surroundings or it can rebind to the heme iron and inhibit enzyme action. Here we have employed Fourier transform infrared (FTIR) photolysis difference spectroscopy at cryogenic temperatures, using the carbon monoxide (CO) and NO stretching bands as local probes of the active site of iNOS. Characteristic changes were observed in the spectra of the heme-bound ligands upon binding of the cofactors. Unlike photolyzed CO, which becomes trapped in well-defined orientations, as indicated by sharp photoproduct bands, photoproduct bands of NO photodissociated from the ferric heme iron were not visible, indicating that NO does not reside in the protein interior in a well-defined location or orientation. This may be favorable for NO release from the enzyme during catalysis because it reduces self-inhibition. Moreover, we used temperature derivative spectroscopy (TDS) with FTIR monitoring to explore the dynamics of NO and carbon monoxide (CO) inside iNOS after photodissociation at cryogenic temperatures. Only a single kinetic photoproduct state was revealed, but no secondary docking sites as in hemoglobins. Interestingly, we observed that intense illumination of six-coordinate ferrous iNOS oxy-NO ruptures the bond between the heme iron and the proximal thiolate to yield five-coordinate ferric iNOS oxy-NO, demonstrating the strong trans effect of the heme-bound NO.
Collapse
Affiliation(s)
- Michael Horn
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics, Karlsruhe, D-76131, Germany
| | - Karin Nienhaus
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics, Karlsruhe, D-76131, Germany
| | - Gerd Ulrich Nienhaus
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics, Karlsruhe, D-76131, Germany
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| |
Collapse
|
15
|
Nishimura R, Shibata T, Tai H, Ishigami I, Yanagisawa S, Ogura T, Neya S, Suzuki A, Yamamoto Y. Effect of the Electron Density of the Heme Fe Atom on the Fe–Histidine Coordination Bond in Deoxy Myoglobin. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2014. [DOI: 10.1246/bcsj.20130331] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
| | | | - Hulin Tai
- Department of Chemistry, University of Tsukuba
| | - Izumi Ishigami
- Picobiology Institute, Graduate School of Life Science, University of Hyogo
| | - Sachiko Yanagisawa
- Picobiology Institute, Graduate School of Life Science, University of Hyogo
| | - Takashi Ogura
- Picobiology Institute, Graduate School of Life Science, University of Hyogo
| | - Saburo Neya
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University
| | - Akihiro Suzuki
- Department of Materials Engineering, Nagaoka National College of Technology
| | | |
Collapse
|
16
|
Woods KN. Using THz time-scale infrared spectroscopy to examine the role of collective, thermal fluctuations in the formation of myoglobin allosteric communication pathways and ligand specificity. SOFT MATTER 2014; 10:4387-4402. [PMID: 24801988 DOI: 10.1039/c3sm53229a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this investigation we use THz time-scale spectroscopy to conduct an initial set of studies on myoglobin with the aim of providing further insight into the global, collective thermal fluctuations in the protein that have been hypothesized to play a prominent role in the dynamic formation of transient ligand channels as well as in shaping the molecular level basis for ligand discrimination. Using the two ligands O2 and CO, we have determined that the perturbation from the heme-ligand complex has a strong influence on the characteristics of the myoglobin collective dynamics that are excited upon binding. Further, the differences detected in the collective protein motions in Mb-O2 compared with those in Mb-CO appear to be intimately tied with the pathways of long-range allosteric communication in the protein, which ultimately determine the trajectories selected by the respective ligands on the path to and from the heme-binding cavity.
Collapse
Affiliation(s)
- K N Woods
- Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
| |
Collapse
|
17
|
Weber B, Nickel E, Horn M, Nienhaus K, Nienhaus GU. Substrate Inhibition in Human Indoleamine 2,3-Dioxygenase. J Phys Chem Lett 2014; 5:756-761. [PMID: 26270849 DOI: 10.1021/jz500220k] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Human indoleamine 2,3-dioxygenase (hIDO) catalyzes the oxidative cleavage of the L-tryptophan (l-Trp) pyrrole ring. Catalysis is inhibited at high substrate concentrations; mechanistic details of this observation are, however, still under debate. Using time-resolved optical spectroscopy, we have analyzed the dynamics of ternary complex formation between hIDO, l-Trp, and a diatomic ligand. The physiological ligand dioxygen (O2) was replaced by carbon monoxide to exclude enzymatic turnover. Quantitative analysis of the kinetics reveals that the ternary complex forms whenever O2 binds first, whereas an l-Trp substrate molecule arriving prior to O2 in the active site causes self-inhibition. Bound l-Trp prevents the ligand from approaching the heme iron and, therefore, impedes formation of the catalytically active ternary complex.
Collapse
Affiliation(s)
| | | | | | | | - G Ulrich Nienhaus
- §Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| |
Collapse
|
18
|
Nienhaus K, Olson JS, Nienhaus GU. An engineered heme-copper center in myoglobin: CO migration and binding. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:1824-31. [PMID: 23459127 DOI: 10.1016/j.bbapap.2013.02.031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 02/19/2013] [Accepted: 02/20/2013] [Indexed: 11/19/2022]
Abstract
We have investigated CO migration and binding in CuBMb, a copper-binding myoglobin double mutant (L29H-F43H), by using Fourier transform infrared spectroscopy and flash photolysis over a wide temperature range. This mutant was originally engineered with the aim to mimic the catalytic site of heme-copper oxidases. Comparison of the wild-type protein Mb and CuBMb shows that the copper ion in the distal pocket gives rise to significant effects on ligand binding to the heme iron. In Mb and copper-free CuBMb, primary and secondary ligand docking sites are accessible upon photodissociation. In copper-bound CuBMb, ligands do not migrate to secondary docking sites but rather coordinate to the copper ion. Ligands entering the heme pocket from the outside normally would not be captured efficiently by the tight distal pocket housing the two additional large imidazole rings. Binding at the Cu ion, however, ensures efficient trapping in CuBMb. The Cu ion also restricts the motions of the His64 side chain, which is the entry/exit door for ligand movement into the active site, and this restriction results in enhanced geminate and slow bimolecular CO rebinding. These results support current mechanistic views of ligand binding in hemoglobins and the role of the CuB in the active of heme-copper oxidases. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.
Collapse
Affiliation(s)
- Karin Nienhaus
- Institute of Applied Physics and Center for Functional Nanostructures, Karlsruhe Institute of Technology, Karlsruhe, Germany
| | | | | |
Collapse
|
19
|
Nienhaus K, Nienhaus GU. A spectroscopic study of structural heterogeneity and carbon monoxide binding in neuroglobin. J Biol Phys 2013; 31:417-32. [PMID: 23345908 DOI: 10.1007/s10867-005-0173-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Neuroglobin (Ngb) is a small globular protein that binds diatomic ligands like oxygen, carbon monoxide (CO) and nitric oxide at a heme prosthetic group. We have performed FTIR spectroscopy in the infrared stretching bands of CO and flash photolysis with monitoring in the electronic heme absorption bands to investigate structural heterogeneity at the active site of Ngb and its effects on CO binding and migration at cryogenic temperatures. Four CO stretching bands were identified; they correspond to discrete conformations that differ in structural details and CO binding properties. Based on a comparison of bound-state and photoproduct IR spectra of the wild-type protein, Ngb distal pocket mutants and myoglobin, we have provided structural interpretations of the conformations associated with the different CO bands. We have also studied ligand migration to the primary docking site, B. Rebinding from this site is governed by very low enthalpy barriers (∼1 kJ/mol), indicating an extremely reactive heme iron. Moreover, we have observed ligand migration to a secondary docking site, C, from which CO rebinding involves higher enthalpy barriers.
Collapse
Affiliation(s)
- Karin Nienhaus
- Department of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany
| | | |
Collapse
|
20
|
Astudillo L, Bernad S, Derrien V, Sebban P, Miksovska J. Conformational dynamics in human neuroglobin: effect of His64, Val68, and Cys120 on ligand migration. Biochemistry 2012; 51:9984-94. [PMID: 23176629 DOI: 10.1021/bi301016u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Neuroglobin belongs to the family of hexacoordinate hemoglobins and has been implicated in the protection of neuronal tissue under hypoxic and ischemic conditions. Here we present transient absorption and photoacoustic calorimetry studies of CO photodissociation and bimolecular rebinding to neuroglobin focusing on the ligand migration process and the role of distal pocket residues (His64 and Val68) and two Cys residues (Cys55 and Cys120). Our results indicate that His64 has a minor impact on the migration of CO between the distal heme pocket and protein exterior, whereas the Val68 side chain regulates the transition of the photodissociated ligand between the distal pocket and internal hydrophobic cavities, which is evident from the increased geminate quantum yield in this mutated protein (Φ(gem) = 0.32 for WT and His64Gln, and Φ(gem) = 0.85 for Val68Phe). The interface between helix G and the A-B loop provides an escape pathway for the photodissociated ligand, which is evident from a decrease in the reaction enthalpy for the transition between the CO-bound hNgb and five-coordinate hNgb in the Cys120Ser mutant (ΔH = -3 ± 4 kcal mol(-1)) compared to that of the WT protein (ΔH = 20 ± 4 kcal mol(-1)). The extensive electrostatic/hydrogen binding network that includes heme propionate groups, Lys67, His64, and Tyr44 not only restricts the heme binding but also modulates the energetics of binding of CO to the five-coordinate hNgb as substitution of His64 with Gln leads to an endothermic association of CO with the five-coordinate hNgb (ΔH = 6 ± 3 kcal mol(-1)).
Collapse
Affiliation(s)
- Luisana Astudillo
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
| | | | | | | | | |
Collapse
|
21
|
Rebinding kinetics of dissociated amino acid ligand and carbon monoxide to ferrous microperoxidase-11 in aqueous solution. Sci China Chem 2012. [DOI: 10.1007/s11426-012-4788-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
22
|
Kim S, Lim M. Protein Conformation-Controlled Rebinding Barrier of NO and Its Binding Trajectories in Myoglobin and Hemoglobin at Room Temperature. J Phys Chem B 2012; 116:5819-30. [DOI: 10.1021/jp300176q] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Seongheun Kim
- Department of Chemistry and Chemistry Institute for
Functional Materials, Pusan National University, Busan 609-735, Korea
| | - Manho Lim
- Department of Chemistry and Chemistry Institute for
Functional Materials, Pusan National University, Busan 609-735, Korea
| |
Collapse
|
23
|
Jasaitis A, Ouellet H, Lambry JC, Martin JL, Friedman JM, Guertin M, Vos MH. Ultrafast heme–ligand recombination in truncated hemoglobin HbO from Mycobacterium tuberculosis: A ligand cage. Chem Phys 2012. [DOI: 10.1016/j.chemphys.2011.04.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
24
|
Pinakoulaki E, Koutsoupakis C, Sawai H, Pavlou A, Kato Y, Asano Y, Aono S. Aldoxime Dehydratase: Probing the Heme Environment Involved in the Synthesis of the Carbon–Nitrogen Triple Bond. J Phys Chem B 2011; 115:13012-8. [DOI: 10.1021/jp205944e] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Eftychia Pinakoulaki
- Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
| | | | - Hitomi Sawai
- Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan
| | - Andrea Pavlou
- Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
| | - Yasuo Kato
- Biotechnology Research Center, Faculty of Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan
| | - Yasuhisa Asano
- Biotechnology Research Center, Faculty of Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan
| | - Shigetoshi Aono
- Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan
| |
Collapse
|
25
|
Nienhaus K, Nickel E, Lu C, Yeh SR, Nienhaus GU. Ligand migration in human indoleamine-2,3 dioxygenase. IUBMB Life 2011; 63:153-9. [PMID: 21445845 DOI: 10.1002/iub.431] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Human indoleamine 2,3-dioxygenase (hIDO), a monomeric heme enzyme, catalyzes the oxidative degradation of L-tryptophan (L-Trp) and other indoleamine derivatives. Its activity follows typical Michaelis-Menten behavior only for L-Trp concentrations up to 50 μM; a further increase in the concentration of L-Trp causes a decrease in the activity. This substrate inhibition of hIDO is a result of the binding of a second L-Trp molecule in an inhibitory substrate binding site of the enzyme. The molecular details of the reaction and the inhibition are not yet known. In the following, we summarize the present knowledge about this heme enzyme.
Collapse
Affiliation(s)
- Karin Nienhaus
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics and Center for Functional Nanostructures, Karlsruhe, Germany.
| | | | | | | | | |
Collapse
|
26
|
Crowley MA, Mollan TL, Abdulmalik OY, Butler AD, Goodwin EF, Sarkar A, Stolle CA, Gow AJ, Olson JS, Weiss MJ. A hemoglobin variant associated with neonatal cyanosis and anemia. N Engl J Med 2011; 364:1837-43. [PMID: 21561349 PMCID: PMC3632254 DOI: 10.1056/nejmoa1013579] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Globin-gene mutations are a rare but important cause of cyanosis. We identified a missense mutation in the fetal Gγ-globin gene (HBG2) in a father and daughter with transient neonatal cyanosis and anemia. This new mutation modifies the ligand-binding pocket of fetal hemoglobin by means of two mechanisms. First, the relatively large side chain of methionine decreases both the affinity of oxygen for binding to the mutant hemoglobin subunit and the rate at which it does so. Second, the mutant methionine is converted to aspartic acid post-translationally, probably through oxidative mechanisms. The presence of this polar amino acid in the heme pocket is predicted to enhance hemoglobin denaturation, causing anemia.
Collapse
Affiliation(s)
- Moira A Crowley
- Division of Neonatology, Case Western Reserve University, Cleveland, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
27
|
Anselmi M, Di Nola A, Amadei A. Kinetics of carbon monoxide migration and binding in solvated neuroglobin as revealed by molecular dynamics simulations and quantum mechanical calculations. J Phys Chem B 2011; 115:2436-46. [PMID: 21332165 DOI: 10.1021/jp110833v] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Neuroglobin (Ngb) is a globular protein that reversibly binds small ligands at the six coordination position of the heme. With respect to other globins similar to myoglobin, Ngb displays some peculiarities as the topological reorganization of the internal cavities coupled to the sliding of the heme, or the binding of the endogenous distal histidine to the heme in the absence of an exogenous ligand. In this Article, by using multiple (independent) molecular dynamics trajectories (about 500 ns in total), the migration pathways of photolized carbon monoxide (CO) within solvated Ngb were analyzed, and a quantitative description of CO migration and corresponding kinetics was obtained. MD results, combined with quantum mechanical calculations on the CO-heme binding-unbinding reaction step in Ngb, allowed construction of a quantitative model representing the relevant steps of CO migration and rebinding.
Collapse
|
28
|
Lautier T, Ezanno P, Baffert C, Fourmond V, Cournac L, Fontecilla-Camps JC, Soucaille P, Bertrand P, Meynial-Salles I, Léger C. The quest for a functional substrate access tunnel in FeFe hydrogenase. Faraday Discuss 2011; 148:385-407; discussion 421-41. [DOI: 10.1039/c004099c] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
29
|
Anselmi M, Di Nola A, Amadei A. The effects of the L29F mutation on the ligand migration kinetics in crystallized myoglobin as revealed by molecular dynamics simulations. Proteins 2010; 79:867-79. [DOI: 10.1002/prot.22924] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Accepted: 10/13/2010] [Indexed: 11/09/2022]
|
30
|
Nienhaus K, Dominici P, Astegno A, Abbruzzetti S, Viappiani C, Nienhaus GU. Ligand migration and binding in nonsymbiotic hemoglobins of Arabidopsis thaliana. Biochemistry 2010; 49:7448-58. [PMID: 20666470 DOI: 10.1021/bi100768g] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
We have studied carbon monoxide (CO) migration and binding in the nonsymbiotic hemoglobins AHb1 and AHb2 of Arabidopsis thaliana using Fourier transform infrared (FTIR) spectroscopy combined with temperature derivative spectroscopy (TDS) at cryogenic temperatures. Both proteins have similar amino acid sequences but display pronounced differences in ligand binding properties, at both physiological and cryogenic temperatures. Near neutral pH, the distal HisE7 side chain is close to the heme-bound ligand in the majority of AHb1-CO molecules, as indicated by a low CO stretching frequency at 1921 cm(-1). In this fraction, two CO docking sites can be populated, the primary site B and the secondary site C. When the pH is lowered, a high-frequency stretching band at approximately 1964 cm(-1) grows at the expense of the low-frequency band, indicating that HisE7 protonates and, concomitantly, moves away from the bound ligand. Geminate rebinding barriers are markedly different for the two conformations, and docking site C is not accessible in the low-pH conformation. Rebinding of NO ligands was observed only from site B of AHb1, regardless of conformation. In AHb2, the HisE7 side chain is removed from the bound ligand; rebinding barriers are low, and CO molecules can populate only primary docking site B. These results are interpreted in terms of differences in the active site structures and physiological functions.
Collapse
Affiliation(s)
- Karin Nienhaus
- Institute of Applied Physics and Center for Functional Nanostructures, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany
| | | | | | | | | | | |
Collapse
|
31
|
Nienhaus K, Nienhaus GU. Ligand dynamics in heme proteins observed by Fourier transform infrared-temperature derivative spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1814:1030-41. [PMID: 20656073 DOI: 10.1016/j.bbapap.2010.07.018] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 07/14/2010] [Accepted: 07/15/2010] [Indexed: 11/29/2022]
Abstract
Fourier transform infrared (FTIR) spectroscopy is a powerful tool for the investigation of protein-ligand interactions in heme proteins. Nitric oxide and carbon monoxide are attractive physiologically relevant ligands because their bond stretching vibrations give rise to strong mid-infrared absorption bands that can be measured with exquisite sensitivity and precision using photolysis difference spectroscopy at cryogenic temperatures. These stretching bands are fine-tuned by electrostatic interactions with the environment and, therefore, ligands can be utilized as local probes of structure and dynamics. Bound to the heme iron, the ligand stretching bands are susceptible to changes in the iron-ligand bond and the electric field at the active site. Upon photolysis, the vibrational bands display changes due to ligand relocation to docking sites within the protein, rotational motions of the ligand in these sites and protein conformational changes. Photolysis difference spectra taken over a wide temperature range (3-300K) using specific temperature protocols for sample photodissociation can provide detailed insights into both protein and ligand dynamics. Moreover, temperature-derivative spectroscopy (TDS) has proven to be a particularly powerful technique to study protein-ligand interactions. The FTIR-TDS technique has been extensively applied to studies of carbon monoxide binding to heme proteins, whereas measurements with nitric oxide are still scarce. Here we describe infrared cryo-spectroscopy and present a variety of applications to the study of protein-ligand interactions in heme proteins. This article is part of a Special Issue entitled: Protein Dynamics: Experimental and Computational Approaches.
Collapse
Affiliation(s)
- Karin Nienhaus
- Karlsruhe Institute of Technology (KIT), Institute of Applied Physics and Center for Functional Nanostructures, Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe, Germany
| | | |
Collapse
|
32
|
Relating diffusion along the substrate tunnel and oxygen sensitivity in hydrogenase. Nat Chem Biol 2009; 6:63-70. [DOI: 10.1038/nchembio.276] [Citation(s) in RCA: 159] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 10/26/2009] [Indexed: 11/08/2022]
|
33
|
Lepeshkevich SV, Dzhagarov BM. Effect of zinc and cadmium ions on structure and function of myoglobin. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:103-9. [DOI: 10.1016/j.bbapap.2008.09.024] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2008] [Revised: 09/26/2008] [Accepted: 09/29/2008] [Indexed: 11/16/2022]
|
34
|
Salter MD, Nienhaus K, Nienhaus GU, Dewilde S, Moens L, Pesce A, Nardini M, Bolognesi M, Olson JS. The apolar channel in Cerebratulus lacteus hemoglobin is the route for O2 entry and exit. J Biol Chem 2008; 283:35689-702. [PMID: 18840607 PMCID: PMC2602902 DOI: 10.1074/jbc.m805727200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2008] [Revised: 09/08/2008] [Indexed: 11/06/2022] Open
Abstract
The major pathway for O2 binding to mammalian myoglobins (Mb) and hemoglobins (Hb) involves transient upward movement of the distal histidine (His-64(E7)), allowing ligand capture in the distal pocket. The mini-globin from Cerebratulus lacteus (CerHb) appears to have an alternative pathway between the E and H helices that is made accessible by loss of the N-terminal A helix. To test this pathway, we examined the effects of changing the size of the E7 gate and closing the end of the apolar channel in CerHb by site-directed mutagenesis. Increasing the size of Gln-44(E7) from Ala to Trp causes variation of association (k'O2) and dissociation (kO2) rate coefficients, but the changes are not systematic. More significantly, the fractions (Fgem approximately 0.05-0.19) and rates (kgem approximately 50-100 micros(-1)) of geminate CO recombination in the Gln-44(E7) mutants are all similar. In contrast, blocking the entrance to the apolar channel by increasing the size of Ala-55(E18) to Phe and Trp causes the following: 1) both k'O2 and kO2 to decrease roughly 4-fold; 2) Fgem for CO to increase from approximately 0.05 to 0.45; and 3) kgem to decrease from approximately 80 to approximately 9 micros(-1), as ligands become trapped in the channel. Crystal structures and low temperature Fourier-transform infrared spectra of Phe-55 and Trp-55 CerHb confirm that the aromatic side chains block the channel entrance, with little effect on the distal pocket. These results provide unambiguous experimental proof that diatomic ligands can enter and exit a globin through an interior channel in preference to the more direct E7 pathway.
Collapse
Affiliation(s)
- Mallory D Salter
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Nienhaus K, Nickel E, Davis MF, Franzen S, Nienhaus GU. Determinants of Substrate Internalization in the Distal Pocket of Dehaloperoxidase Hemoglobin of Amphitrite ornata. Biochemistry 2008; 47:12985-94. [DOI: 10.1021/bi801564r] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Karin Nienhaus
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801
| | - Elena Nickel
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801
| | - Michael F. Davis
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801
| | - Stefan Franzen
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801
| | - G. Ulrich Nienhaus
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, and Department of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801
| |
Collapse
|
36
|
Influence of proline on the thermostability of the active site and membrane arrangement of transmembrane proteins. Biophys J 2008; 95:4384-95. [PMID: 18658225 DOI: 10.1529/biophysj.108.136747] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proline residues play a fundamental and subtle role in the dynamics, structure, and function in many membrane proteins. Temperature derivative spectroscopy and differential scanning calorimetry have been used to determine the effect of proline substitution in the structural stability of the active site and transmembrane arrangement of bacteriorhodopsin. We have analyzed the Pro-to-Ala mutation for the helix-embedded prolines Pro50, Pro91, and Pro186 in the native membrane environment. This information has been complemented with the analysis of the respective crystallographic structures by the FoldX force field. Differential scanning calorimetry allowed us to determine distorted membrane arrangement for P50A and P186A. The protein stability was severely affected for P186A and P91A. In the case of Pro91, a single point mutation is capable of strongly slowing down the conformational diffusion along the denaturation coordinate, becoming a barrier-free downhill process above 371 K. Temperature derivative spectroscopy, applied for first time to study thermal stability of proteins, has been used to monitor the stability of the active site of bacteriorhodopsin. The mutation of Pro91 and Pro186 showed the most striking effects on the retinal binding pocket. These residues are the Pro in closer contact to the active site (activation energies for retinal release of 60.1 and 76.8 kcal/mol, respectively, compared to 115.8 kcal/mol for WT). FoldX analysis of the protein crystal structures indicates that the Pro-to-Ala mutations have both local and long-range effects on the structural stability of residues involved in the architecture of the protein and the active site and in the proton pumping function. Thus, this study provides a complete overview of the substitution effect of helix-embedded prolines in the thermodynamic and dynamic stability of a membrane protein, also related to its structure and function.
Collapse
|
37
|
Use of the Conjugate Peak Refinement Algorithm for Identification of Ligand‐Binding Pathways in Globins. Methods Enzymol 2008; 437:417-37. [DOI: 10.1016/s0076-6879(07)37021-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
|
38
|
Nienhaus K, Nienhaus GU. Ligand dynamics in heme proteins observed by Fourier transform infrared spectroscopy at cryogenic temperatures. Methods Enzymol 2008; 437:347-78. [PMID: 18433637 DOI: 10.1016/s0076-6879(07)37018-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Fourier transform infrared spectroscopy is a powerful tool for the investigation of protein-ligand interactions in heme proteins. From the variety of ligands that bind to the heme iron, nitric oxide and carbon monoxide are particularly attractive, as their bond-stretching vibrations give rise to strong mid-infrared absorption bands that can be measured with exquisite sensitivity and precision using photolysis difference spectroscopy at cryogenic temperatures. These stretching bands are fine-tuned by electrostatic interactions with the environment and, therefore, the ligands can be utilized as local probes of structure and dynamics. Bound to the heme iron, the ligand-stretching bands are susceptible to changes in the iron-ligand bond and the electric field at the active site. Upon photolysis, the vibrational bands reveal changes due to ligand relocation to docking sites within the protein, rotational motions of the ligand in these sites, and protein conformational changes. Photolysis difference spectra taken over a wide temperature range (3-300 K) using specific temperature protocols for sample photodissociation thus can provide detailed insights into both protein and ligand dynamics. Moreover, temperature-derivative spectroscopy has proven to be a particularly powerful technique to study protein-ligand interactions. This technique has been extensively applied to studies of carbon monoxide binding to heme proteins, whereas measurements with nitric oxide are still scarce. This chapter describes infrared cryospectroscopy techniques and presents examples that demonstrate their applicability to nitric oxide binding to heme proteins.
Collapse
Affiliation(s)
- Karin Nienhaus
- Institute of Biophysics, University of Ulm, Ulm, Germany
| | | |
Collapse
|
39
|
|
40
|
Nienhaus K, Palladino P, Nienhaus GU. Structural Dynamics of Myoglobin: FTIR-TDS Study of NO Migration and Binding†. Biochemistry 2007; 47:935-48. [DOI: 10.1021/bi701935v] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Karin Nienhaus
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, and Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Il 61801
| | - Pasquale Palladino
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, and Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Il 61801
| | - G. Ulrich Nienhaus
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany, and Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Il 61801
| |
Collapse
|
41
|
Nienhaus K, Knapp JE, Palladino P, Royer WE, Nienhaus GU. Ligand migration and binding in the dimeric hemoglobin of Scapharca inaequivalvis. Biochemistry 2007; 46:14018-31. [PMID: 18001141 DOI: 10.1021/bi7016798] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using Fourier transform infrared (FTIR) spectroscopy combined with temperature derivative spectroscopy (TDS) at cryogenic temperatures, we have studied CO binding to the heme and CO migration among cavities in the interior of the dimeric hemoglobin of Scapharca inaequivalvis (HbI) after photodissociation. By combining these studies with X-ray crystallography, three transient ligand docking sites were identified: a primary docking site B in close vicinity to the heme iron, and two secondary docking sites C and D corresponding to the Xe4 and Xe2 cavities of myoglobin. To assess the relevance of these findings for physiological binding, we also performed flash photolysis experiments on HbICO at room temperature and equilibrium binding studies with dioxygen. Our results show that the Xe4 and Xe2 cavities serve as transient docking sites for unbound ligands in the protein, but not as way stations on the entry/exit pathway. For HbI, the so-called histidine gate mechanism proposed for other globins appears as a plausible entry/exit route as well.
Collapse
Affiliation(s)
- Karin Nienhaus
- Institute of Biophysics, University of Ulm, 89069 Ulm, Germany
| | | | | | | | | |
Collapse
|
42
|
Bredenbeck J, Helbing J, Kolano C, Hamm P. Ultrafast 2D–IR Spectroscopy of Transient Species. Chemphyschem 2007; 8:1747-56. [PMID: 17615613 DOI: 10.1002/cphc.200700148] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Multidimensional spectroscopic experiments offer fascinating insights into molecular structure and dynamics in the field of NMR spectroscopy. With the introduction of ultrafast two-dimensional infrared spectroscopy (2D-IR), multidimensional concepts have entered the optical domain, measuring couplings and correlations between molecular vibrations with femtosecond time resolution. In the transient 2D-IR (T2D-IR) experiments described in this minireview we exploit the high time resolution of 2D-IR to study transient species during fast nonequilibrium processes in real time. Information on molecular structure and dynamics is obtained that is not available from one-dimensional spectroscopy. We discuss examples from chemistry, physics and biophysics.
Collapse
Affiliation(s)
- Jens Bredenbeck
- Physikalisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
| | | | | | | |
Collapse
|
43
|
Nienhaus K, Deng P, Belyea J, Franzen S, Nienhaus GU. Spectroscopic study of substrate binding to the carbonmonoxy form of dehaloperoxidase from Amphitrite ornata. J Phys Chem B 2007; 110:13264-76. [PMID: 16805641 DOI: 10.1021/jp060278z] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Dehaloperoxidase (DHP) is a globular heme enzyme found in the marine worm Amphitrite ornata that can catalyze the dehalogenation of halophenols to the corresponding quinones by using hydrogen peroxide as a cosubstrate. Its three-dimensional fold is surprisingly similar to that of the oxygen storage protein myoglobin (Mb). A key structural feature common to both DHP and Mb is the existence of multiple conformations of the distal histidine. In DHP, the conformational flexibility may be involved in promotion of substrate and cosubstrate entry and exit. Here we have explored the dynamics of substrate binding in DHP using Fourier transform infrared spectroscopy and flash photolysis. A number of discrete conformations at the active site were identified from the appearance of multiple CO absorbance bands in the infrared region of the spectrum. Upon photolysis at cryogenic temperatures, the CO molecules are trapped at docking sites within the protein matrix, as inferred from the appearance of several photoproduct bands characteristic of each site. Substrate binding stabilizes the protein by approximately 20 kJ/mol. The low yield of substrate-bound DHP at ambient temperature points toward a steric inhibition of substrate binding by carbon monoxide.
Collapse
Affiliation(s)
- Karin Nienhaus
- Department of Biophysics, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
| | | | | | | | | |
Collapse
|
44
|
Kondrashov DA, Montfort WR. Nonequilibrium dynamics simulations of nitric oxide release: comparative study of nitrophorin and myoglobin. J Phys Chem B 2007; 111:9244-52. [PMID: 17622170 DOI: 10.1021/jp071136n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nitrophorin 4 (NP4) is a heme protein that reversibly binds nitric oxide (NO), with release rates modulated by pH change. High-resolution structures of NP4 revealed that pH changes and NO binding induce a large conformational rearrangement in two loops that serve to protect the heme-bound NO molecule from solvent. We used extended (110 ns) molecular dynamics simulations of NP4 at pH 5 and pH 7, modeled by selective deprotonation of acidic groups. Conformational and dynamic changes were observed, consistent with those found in the crystal. Further, major solvent movement and NO escape were observed at pH 7, while the ligand remained in the heme binding pocket at pH 5. As a control, we also performed molecular dynamics (MD) simulations of sperm whale myoglobin, where NO migration into the interior cavities of the protein was observed, consistent with previous reports. We constructed a kinetic model of ligand escape to quantitatively relate the microscopic rate constants to the observed rates, and tested the predictions against the experimental data. The results suggest that release rates of diatomic molecules from heme proteins can be varied by several orders of magnitude through modest adjustments in geminate rebinding and gating behavior.
Collapse
Affiliation(s)
- Dmitry A Kondrashov
- Graduate Program in Applied Mathematics and Department of Biochemistry & Molecular Biophysics, University of Arizona, Tucson, Arizona 85721, USA.
| | | |
Collapse
|
45
|
Deng P, Nienhaus K, Palladino P, Olson JS, Blouin G, Moens L, Dewilde S, Geuens E, Nienhaus GU. Transient ligand docking sites in Cerebratulus lacteus mini-hemoglobin. Gene 2007; 398:208-23. [PMID: 17531406 PMCID: PMC1986801 DOI: 10.1016/j.gene.2007.01.037] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2006] [Revised: 01/27/2007] [Accepted: 01/30/2007] [Indexed: 11/22/2022]
Abstract
The monomeric hemoglobin of the nemertean worm Cerebratulus lacteus functions as an oxygen storage protein to maintain neural activity under hypoxic conditions. It shares a large, apolar matrix tunnel with other small hemoglobins, which has been implicated as a potential ligand migration pathway. Here we explore ligand migration and binding within the distal heme pocket, to which the tunnel provides access to ligands from the outside. FTIR/TDS experiments performed at cryogenic temperatures reveal the presence of three transient ligand docking sites within the distal pocket, the primary docking site B on top of pyrrole C and secondary sites C and D. Site C is assigned to a cavity adjacent to the distal portion of the heme pocket, surrounded by the B and E helices. It has an opening to the apolar tunnel and is expected to be on the pathway for ligand entry and exit, whereas site D, circumscribed by TyrB10, GlnE7, and the CD corner, most likely is located on a side pathway of ligand migration. Flash photolysis experiments at ambient temperatures indicate that the rate-limiting step for ligand binding to CerHb is migration through the apolar channel to site C. Movement from C to B and iron-ligand bond formation involve low energy barriers and thus are very rapid processes in the wt protein.
Collapse
Affiliation(s)
- Pengchi Deng
- Institute of Biophysics, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
46
|
Anselmi M, Aschi M, Di Nola A, Amadei A. Theoretical characterization of carbon monoxide vibrational spectrum in sperm whale myoglobin distal pocket. Biophys J 2007; 92:3442-7. [PMID: 17307822 PMCID: PMC1853160 DOI: 10.1529/biophysj.106.098442] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In this article we use the perturbed matrix method and an extended molecular dynamics sampling of the carbon monoxide (CO) in the myoglobin distal pocket to characterize the CO vibrational spectrum and hence to relate its spectroscopic features with the atomic-molecular behavior. Results show the accuracy of the method employed and confirm the assignment of the spectroscopic B1 and B2 states proposed by Lim et al.
Collapse
|
47
|
Bredenbeck J, Helbing J, Nienhaus K, Nienhaus GU, Hamm P. Protein ligand migration mapped by nonequilibrium 2D-IR exchange spectroscopy. Proc Natl Acad Sci U S A 2007; 104:14243-8. [PMID: 17261808 PMCID: PMC1964829 DOI: 10.1073/pnas.0607758104] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
2D-IR exchange spectroscopy has been introduced recently to map chemical exchange networks in equilibrium with subpicosecond time resolution. Here, we demonstrate the generalization of 2D-IR exchange spectroscopy to nonequilibrium systems and its application to map light-triggered migration of ligands between different sites in a protein. Within picoseconds after a photodissociating laser pulse, carbon monoxide ligands relocate from their binding site A at the heme prosthetic group of myoglobin to a primary docking site B in the distal heme pocket. Multiple CO stretching bands are observed for the CO ligand in sites A and B, indicating that several distinct conformational substates of the myoglobin:ligand complex coexist in solution. Exchange cross-peaks between the bands associated with substates of heme-bound CO and photodissociated CO in the primary docking site reveal the substate connectivity at physiological temperature.
Collapse
Affiliation(s)
- Jens Bredenbeck
- Physikalisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
| | | | | | | | | |
Collapse
|
48
|
Nonequilibrium 2D-IR Exchange Spectroscopy: Ligand Migration in Proteins. ULTRAFAST PHENOMENA XV 2007. [DOI: 10.1007/978-3-540-68781-8_122] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
|
49
|
Silkstone G, Jasaitis A, Wilson MT, Vos MH. Ligand Dynamics in an Electron Transfer Protein. J Biol Chem 2007; 282:1638-49. [PMID: 17114183 DOI: 10.1074/jbc.m605760200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Substitution of the heme coordination residue Met-80 of the electron transport protein yeast iso-1-cytochrome c allows external ligands like CO to bind and thus increase the effective redox potential. This mutation, in principle, turns the protein into a quasi-native photoactivable electron donor. We have studied the kinetic and spectral characteristics of geminate recombination of heme and CO in a series of single M80X (X = Ala, Ser, Asp, Arg) mutants, using femtosecond transient absorption spectroscopy. In these proteins, all geminate recombination occurs on the picosecond and early nanosecond time scale, in a multiphasic manner, in which heme relaxation takes place on the same time scale. The extent of geminate recombination varies from >99% (Ala, Ser) to approximately 70% (Arg), the latter value being in principle low enough for electron injection studies. The rates and extent of the CO geminate recombination phases are much higher than in functional ligand-binding proteins like myoglobin, presumably reflecting the rigid and hydrophobic properties of the heme environment, which are optimized for electron transfer. Thus, the dynamics of CO recombination in cytochrome c are a tool for studying the heme pocket, in a similar way as NO in myoglobin. We discuss the differences in the CO kinetics between the mutants in terms of the properties of the heme environment and strategies to enhance the CO escape yield. Experiments on double mutants in which Phe-82 is replaced by Asp or Gly as well as the M80D substitution indicate that such steric changes substantially increase the motional freedom-dissociated CO.
Collapse
Affiliation(s)
- Gary Silkstone
- Department of Biological Sciences, Wivenhoe Park, University of Essex, Colchester CO4 3SQ, United Kingdom
| | | | | | | |
Collapse
|
50
|
Ionascu D, Gruia F, Ye X, Yu A, Rosca F, Beck C, Demidov A, Olson JS, Champion PM. Temperature-dependent studies of NO recombination to heme and heme proteins. J Am Chem Soc 2005; 127:16921-34. [PMID: 16316238 PMCID: PMC2553725 DOI: 10.1021/ja054249y] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The rebinding kinetics of NO to the heme iron of myoglobin (Mb) is investigated as a function of temperature. Below 200 K, the transition-state enthalpy barrier associated with the fastest (approximately 10 ps) recombination phase is found to be zero and a slower geminate phase (approximately 200 ps) reveals a small enthalpic barrier (approximately 3 +/- 1 kJ/mol). Both of the kinetic rates slow slightly in the myoglobin (Mb) samples above 200 K, suggesting that a small amount of protein relaxation takes place above the solvent glass transition. When the temperature dependence of the NO recombination in Mb is studied under conditions where the distal pocket is mutated (e.g., V68W), the rebinding kinetics lack the slow phase. This is consistent with a mechanism where the slower (approximately 200 ps) kinetic phase involves transitions of the NO ligand into the distal heme pocket from a more distant site (e.g., in or near the Xe4 cavity). Comparison of the temperature-dependent NO rebinding kinetics of native Mb with that of the bare heme (PPIX) in glycerol reveals that the fast (enthalpically barrierless) NO rebinding process observed below 200 K is independent of the presence or absence of the proximal histidine ligand. In contrast, the slowing of the kinetic rates above 200 K in MbNO disappears in the absence of the protein. Generally, the data indicate that, in contrast to CO, the NO ligand binds to the heme iron through a "harpoon" mechanism where the heme iron out-of-plane conformation presents a negligible enthalpic barrier to NO rebinding. These observations strongly support a previous analysis (Srajer et al. J. Am. Chem. Soc. 1988, 110, 6656-6670) that primarily attributes the low-temperature stretched exponential rebinding of MbCO to a quenched distribution of heme geometries. A simple model, consistent with this prior analysis, is presented that explains a variety of MbNO rebinding experiments, including the dependence of the kinetic amplitudes on the pump photon energy.
Collapse
Affiliation(s)
- Dan Ionascu
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | - Flaviu Gruia
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | - Xiong Ye
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | - Anchi Yu
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | - Florin Rosca
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | - Chris Beck
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | - Andrey Demidov
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| | | | - Paul M. Champion
- Dept. of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston 02115
| |
Collapse
|