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Paramagnetic resonance investigation of mono- and di-manganese-containing systems in biochemistry. Methods Enzymol 2022; 666:315-372. [DOI: 10.1016/bs.mie.2022.02.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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2
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Pastore AJ, Teo RD, Montoya A, Burg MJ, Twahir UT, Bruner SD, Beratan DN, Angerhofer A. Oxalate decarboxylase uses electron hole hopping for catalysis. J Biol Chem 2021; 297:100857. [PMID: 34097877 PMCID: PMC8254039 DOI: 10.1016/j.jbc.2021.100857] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 05/28/2021] [Accepted: 06/03/2021] [Indexed: 01/16/2023] Open
Abstract
The hexameric low-pH stress response enzyme oxalate decarboxylase catalyzes the decarboxylation of the oxalate mono-anion in the soil bacterium Bacillus subtilis. A single protein subunit contains two Mn-binding cupin domains, and catalysis depends on Mn(III) at the N-terminal site. The present study suggests a mechanistic function for the C-terminal Mn as an electron hole donor for the N-terminal Mn. The resulting spatial separation of the radical intermediates directs the chemistry toward decarboxylation of the substrate. A π-stacked tryptophan pair (W96/W274) links two neighboring protein subunits together, thus reducing the Mn-to-Mn distance from 25.9 Å (intrasubunit) to 21.5 Å (intersubunit). Here, we used theoretical analysis of electron hole-hopping paths through redox-active sites in the enzyme combined with site-directed mutagenesis and X-ray crystallography to demonstrate that this tryptophan pair supports effective electron hole hopping between the C-terminal Mn of one subunit and the N-terminal Mn of the other subunit through two short hops of ∼8.5 Å. Replacement of W96, W274, or both with phenylalanine led to a large reduction in catalytic efficiency, whereas replacement with tyrosine led to recovery of most of this activity. W96F and W96Y mutants share the wildtype tertiary structure. Two additional hole-hopping networks were identified leading from the Mn ions to the protein surface, potentially protecting the enzyme from high Mn oxidation states during turnover. Our findings strongly suggest that multistep hole-hopping transport between the two Mn ions is required for enzymatic function, adding to the growing examples of proteins that employ aromatic residues as hopping stations.
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Affiliation(s)
- Anthony J Pastore
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - Ruijie D Teo
- Department of Chemistry, Duke University, Durham, North Carolina, USA
| | - Alvaro Montoya
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - Matthew J Burg
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - Umar T Twahir
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - Steven D Bruner
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - David N Beratan
- Department of Chemistry, Duke University, Durham, North Carolina, USA.
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Marsden SR, Mestrom L, Bento I, Hagedoorn P, McMillan DGG, Hanefeld U. CH‐π Interactions Promote the Conversion of Hydroxypyruvate in a Class II Pyruvate Aldolase. Adv Synth Catal 2019. [DOI: 10.1002/adsc.201900205] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Stefan R. Marsden
- Biokatalyse, Afdeling Biotechnologie Technische Universiteit Delft van der Maasweg 9 2629HZ Delft, The Netherlands
- EMBL Hamburg Notkestrasse 85 22607 Hamburg Germany
| | - Luuk Mestrom
- Biokatalyse, Afdeling Biotechnologie Technische Universiteit Delft van der Maasweg 9 2629HZ Delft, The Netherlands
| | - Isabel Bento
- EMBL Hamburg Notkestrasse 85 22607 Hamburg Germany
| | - Peter‐Leon Hagedoorn
- Biokatalyse, Afdeling Biotechnologie Technische Universiteit Delft van der Maasweg 9 2629HZ Delft, The Netherlands
| | - Duncan G. G. McMillan
- Biokatalyse, Afdeling Biotechnologie Technische Universiteit Delft van der Maasweg 9 2629HZ Delft, The Netherlands
| | - Ulf Hanefeld
- Biokatalyse, Afdeling Biotechnologie Technische Universiteit Delft van der Maasweg 9 2629HZ Delft, The Netherlands
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4
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Banerjee A, Tolla AS, Stjepanovic S, Sevilla MD, Goodsell JL, Angerhofer A, Brennessel WW, Loloee R, Chavez FA. Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes. Inorganica Chim Acta 2019; 486:546-555. [PMID: 33981118 PMCID: PMC8112617 DOI: 10.1016/j.ica.2018.11.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We report the synthesis of [Mn(tacud)2](OTf)2 (1) (tacud = 1,4,8-triazacycloundecane), [Mn(tacd)2](OTf)2 (2) (tacd = 1,4,7-triazacyclodecane), and [Mn(tacn)2](OTf)2 (3) (tacn = 1,4,7-triazacyclononane). Electrochemical measurements on the MnIII/II redox couple show that complex 1 has the largest anodic potential of the set (E 1/2 = 1.16 V vs NHE, ΔE p = 106 mV) compared to 2 (E 1/2 = 0.95 V, ΔE p = 108 mV) and 3 (E 1/2 = 0.93 V, ΔE p = 96 mV). This is due to the fact that 1 has the fewest 5-membered chelate rings and thus is least stabilized. Magnetic studies of 1-3 revealed that all complexes remain high spin throughout the temperature range investigated (2 - 300 K). X-band EPR investigations in methanol glass indicated that the manganese(II) centers for 2 and 3 resided in a more distorted octahedral geometric configuration compared to 1. To ease spectral interpretation and extract ZFS parameters, we performed high-frequency high-field EPR (HFEPR) at frequencies above 200 GHz and a field of 7.5 T. Simulation of the spectral data yielded g = 2.0013 and D = -0.031 cm-1 for 1, g = 2.0008, D = -0.0824 cm-1, |E/D| = 0.12 for 2, and g = 2.00028, D = -0.0884 cm-1 for 3. These results are consistent with 3 possessing the most distorted geometry. Calculations (PBE0/6-31G(d)) were performed on 1-3. Results show that 1 has the largest HOMO-LUMO gap energy (6.37 eV) compared to 2 (6.12 eV) and 3 (6.26 eV). Complex 1 also has the lowest HOMO energies indicating higher stability.
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Affiliation(s)
- Atanu Banerjee
- Department of Chemistry, Oakland University, Rochester, MI 48309-4477, USA
| | - Azam S Tolla
- Department of Chemistry, Oakland University, Rochester, MI 48309-4477, USA
| | | | - Michael D Sevilla
- Department of Chemistry, Oakland University, Rochester, MI 48309-4477, USA
| | - Justin L Goodsell
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
| | | | | | - Reza Loloee
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-1322, USA
| | - Ferman A Chavez
- Department of Chemistry, Oakland University, Rochester, MI 48309-4477, USA
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5
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Zhu W, Reinhardt LA, Richards NGJ. Second-Shell Hydrogen Bond Impacts Transition-State Structure in Bacillus subtilis Oxalate Decarboxylase. Biochemistry 2018; 57:3425-3432. [DOI: 10.1021/acs.biochem.8b00214] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Wen Zhu
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, United Kingdom
| | - Laurie A. Reinhardt
- Institute for Enzyme Research and Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53726, United States
| | - Nigel G. J. Richards
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, United Kingdom
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6
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Biological functions controlled by manganese redox changes in mononuclear Mn-dependent enzymes. Essays Biochem 2017; 61:259-270. [PMID: 28487402 DOI: 10.1042/ebc20160070] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 03/05/2017] [Accepted: 03/17/2017] [Indexed: 02/06/2023]
Abstract
Remarkably few enzymes are known to employ a mononuclear manganese ion that undergoes changes in redox state during catalysis. Many questions remain to be answered about the role of substrate binding and/or protein environment in modulating the redox properties of enzyme-bound Mn(II), the nature of the dioxygen species involved in the catalytic mechanism, and how these enzymes acquire Mn(II) given that many other metal ions in the cell form more stable protein complexes. Here, we summarize current knowledge concerning the structure and mechanism of five mononuclear manganese-dependent enzymes: superoxide dismutase, oxalate oxidase (OxOx), oxalate decarboxylase (OxDC), homoprotocatechuate 3,4-dioxygenase, and lipoxygenase (LOX). Spectroscopic measurements and/or computational studies suggest that Mn(III)/Mn(II) are the catalytically active oxidation states of the metal, and the importance of 'second-shell' hydrogen bonding interactions with metal ligands has been demonstrated for a number of examples. The ability of these enzymes to modulate the redox properties of the Mn(III)/Mn(II) couple, thereby allowing them to generate substrate-based radicals, appears essential for accessing diverse chemistries of fundamental importance to organisms in all branches of life.
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Twahir UT, Ozarowski A, Angerhofer A. Redox Cycling, pH Dependence, and Ligand Effects of Mn(III) in Oxalate Decarboxylase from Bacillus subtilis. Biochemistry 2016; 55:6505-6516. [DOI: 10.1021/acs.biochem.6b00891] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Umar T. Twahir
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611-7200, United States
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | - Alexander Angerhofer
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611-7200, United States
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Vertregt F, Torrelo G, Trunk S, Wiltsche H, Hagen WR, Hanefeld U, Steiner K. EPR Study of Substrate Binding to Mn(II) in Hydroxynitrile Lyase from Granulicella tundricola. ACS Catal 2016. [DOI: 10.1021/acscatal.6b01204] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Femke Vertregt
- Biokatalyse,
Afdeling Biotechnologie, Technische Universiteit Delft, van der Maasweg
9, 2629HZ Delft, The Netherlands
| | - Guzman Torrelo
- Biokatalyse,
Afdeling Biotechnologie, Technische Universiteit Delft, van der Maasweg
9, 2629HZ Delft, The Netherlands
| | - Sarah Trunk
- Austrian Centre
of Industrial Biotechnology GmbH, Petersgasse
14/4, 8010 Graz, Austria
| | - Helmar Wiltsche
- Institute
of Analytical Chemistry and Food Chemistry, TU Graz, Stremayrgasse
9/III, 8010 Graz, Austria
| | - Wilfred R. Hagen
- Biokatalyse,
Afdeling Biotechnologie, Technische Universiteit Delft, van der Maasweg
9, 2629HZ Delft, The Netherlands
| | - Ulf Hanefeld
- Biokatalyse,
Afdeling Biotechnologie, Technische Universiteit Delft, van der Maasweg
9, 2629HZ Delft, The Netherlands
| | - Kerstin Steiner
- Austrian Centre
of Industrial Biotechnology GmbH, Petersgasse
14/4, 8010 Graz, Austria
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9
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Zhu W, Easthon LM, Reinhardt LA, Tu C, Cohen SE, Silverman DN, Allen KN, Richards NGJ. Substrate Binding Mode and Molecular Basis of a Specificity Switch in Oxalate Decarboxylase. Biochemistry 2016; 55:2163-73. [PMID: 27014926 PMCID: PMC4854488 DOI: 10.1021/acs.biochem.6b00043] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Oxalate
decarboxylase (OxDC) catalyzes the conversion of oxalate
into formate and carbon dioxide in a remarkable reaction that requires
manganese and dioxygen. Previous studies have shown that replacing
an active-site loop segment Ser161-Glu162-Asn163-Ser164 in the N-terminal domain of OxDC with
the cognate residues Asp161-Ala162-Ser-163-Asn164 of an evolutionarily related, Mn-dependent
oxalate oxidase gives a chimeric variant (DASN) that exhibits significantly
increased oxidase activity. The mechanistic basis for this change
in activity has now been investigated using membrane inlet mass spectrometry
(MIMS) and isotope effect (IE) measurements. Quantitative analysis
of the reaction stoichiometry as a function of oxalate concentration,
as determined by MIMS, suggests that the increased oxidase activity
of the DASN OxDC variant is associated with only a small fraction
of the enzyme molecules in solution. In addition, IE measurements
show that C–C bond cleavage in the DASN OxDC variant proceeds
via the same mechanism as in the wild-type enzyme, even though the
Glu162 side chain is absent. Thus, replacement of the loop
residues does not modulate the chemistry of the enzyme-bound Mn(II)
ion. Taken together, these results raise the possibility that the
observed oxidase activity of the DASN OxDC variant arises from an
increased level of access of the solvent to the active site during
catalysis, implying that the functional role of Glu162 is
to control loop conformation. A 2.6 Å resolution X-ray crystal
structure of a complex between oxalate and the Co(II)-substituted
ΔE162 OxDC variant, in which Glu162 has been deleted
from the active site loop, reveals the likely mode by which the substrate
coordinates the catalytically active Mn ion prior to C–C bond
cleavage. The “end-on” conformation of oxalate observed
in the structure is consistent with the previously published V/K IE data and provides an empty coordination
site for the dioxygen ligand that is thought to mediate the formation
of Mn(III) for catalysis upon substrate binding.
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Affiliation(s)
- Wen Zhu
- Department of Chemistry & Chemical Biology, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States
| | - Lindsey M Easthon
- Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States
| | - Laurie A Reinhardt
- Department of Biochemistry, University of Wisconsin , Madison, Wisconsin 53726, United States
| | - Chingkuang Tu
- Department of Pharmacology & Therapeutics, University of Florida , Gainesville, Florida 32610, United States
| | - Steven E Cohen
- Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States
| | - David N Silverman
- Department of Pharmacology & Therapeutics, University of Florida , Gainesville, Florida 32610, United States
| | - Karen N Allen
- Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States
| | - Nigel G J Richards
- Department of Chemistry & Chemical Biology, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States
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Leto DF, Massie AA, Colmer HE, Jackson TA. X-Band Electron Paramagnetic Resonance Comparison of Mononuclear Mn(IV)-oxo and Mn(IV)-hydroxo Complexes and Quantum Chemical Investigation of Mn(IV) Zero-Field Splitting. Inorg Chem 2016; 55:3272-82. [PMID: 27002928 DOI: 10.1021/acs.inorgchem.5b02309] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
X-band electron paramagnetic resonance (EPR) spectroscopy was used to probe the ground-state electronic structures of mononuclear Mn(IV) complexes [Mn(IV)(OH)2(Me2EBC)](2+) and [Mn(IV)(O)(OH)(Me2EBC)](+). These compounds are known to effect C-H bond oxidation reactions by a hydrogen-atom transfer mechanism. They provide an ideal system for comparing Mn(IV)-hydroxo versus Mn(IV)-oxo motifs, as they differ by only a proton. Simulations of 5 K EPR data, along with analysis of variable-temperature EPR signal intensities, allowed for the estimation of ground-state zero-field splitting (ZFS) and (55)Mn hyperfine parameters for both complexes. From this analysis, it was concluded that the Mn(IV)-oxo complex [Mn(IV)(O)(OH)(Me2EBC)](+) has an axial ZFS parameter D (D = +1.2(0.4) cm(-1)) and rhombicity (E/D = 0.22(1)) perturbed relative to the Mn(IV)-hydroxo analogue [Mn(IV)(OH)2(Me2EBC)](2+) (|D| = 0.75(0.25) cm(-1); E/D = 0.15(2)), although the complexes have similar (55)Mn values (a = 7.7 and 7.5 mT, respectively). The ZFS parameters for [Mn(IV)(OH)2(Me2EBC)](2+) were compared with values obtained previously through variable-temperature, variable-field magnetic circular dichroism (VTVH MCD) experiments. While the VTVH MCD analysis can provide a reasonable estimate of the magnitude of D, the E/D values were poorly defined. Using the ZFS parameters reported for these complexes and five other mononuclear Mn(IV) complexes, we employed coupled-perturbed density functional theory (CP-DFT) and complete active space self-consistent field (CASSCF) calculations with second-order n-electron valence-state perturbation theory (NEVPT2) correction, to compare the ability of these two quantum chemical methods for reproducing experimental ZFS parameters for Mn(IV) centers. The CP-DFT approach was found to provide reasonably acceptable values for D, whereas the CASSCF/NEVPT2 method fared worse, considerably overestimating the magnitude of D in several cases. Both methods were poor in reproducing experimental E/D values. Overall, this work adds to the limited investigations of Mn(IV) ground-state properties and provides an initial assessment for calculating Mn(IV) ZFS parameters with quantum chemical methods.
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Affiliation(s)
- Domenick F Leto
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
| | - Allyssa A Massie
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
| | - Hannah E Colmer
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
| | - Timothy A Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
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Zhu W, Wilcoxen J, Britt RD, Richards NGJ. Formation of Hexacoordinate Mn(III) in Bacillus subtilis Oxalate Decarboxylase Requires Catalytic Turnover. Biochemistry 2016; 55:429-34. [PMID: 26744902 DOI: 10.1021/acs.biochem.5b01340] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Oxalate decarboxylase (OxDC) catalyzes the disproportionation of oxalic acid monoanion into CO2 and formate. The enzyme has long been hypothesized to utilize dioxygen to form mononuclear Mn(III) or Mn(IV) in the catalytic site during turnover. Recombinant OxDC, however, contains only tightly bound Mn(II), and direct spectroscopic detection of the metal in higher oxidation states under optimal catalytic conditions (pH 4.2) has not yet been reported. Using parallel mode electron paramagnetic resonance spectroscopy, we now show that substantial amounts of Mn(III) are indeed formed in OxDC, but only in the presence of oxalate and dioxygen under acidic conditions. These observations provide the first direct support for proposals in which Mn(III) removes an electron from the substrate to yield a radical intermediate in which the barrier to C-C bond cleavage is significantly decreased. Thus, OxDC joins a small list of enzymes capable of stabilizing and controlling the reactivity of the powerful oxidizing species Mn(III).
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Affiliation(s)
- Wen Zhu
- Department of Chemistry & Chemical Biology, Indiana University Purdue University Indianapolis , Indianapolis, Indiana 46202, United States
| | - Jarett Wilcoxen
- Department of Chemistry, University of California , Davis, California 95616, United States
| | - R David Britt
- Department of Chemistry, University of California , Davis, California 95616, United States
| | - Nigel G J Richards
- Department of Chemistry & Chemical Biology, Indiana University Purdue University Indianapolis , Indianapolis, Indiana 46202, United States
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Immobilization of Bacillus subtilis oxalate decarboxylase on a Zn-IMAC resin. Biochem Biophys Rep 2015; 4:98-103. [PMID: 29124192 PMCID: PMC5668902 DOI: 10.1016/j.bbrep.2015.08.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 08/19/2015] [Accepted: 08/24/2015] [Indexed: 11/21/2022] Open
Abstract
Oxalate decarboxylase, a bicupin enzyme coordinating two essential manganese ions per subunit, catalyzes the decomposition of oxalate into carbon dioxide and formate in the presence of oxygen. Current efforts to elucidate its catalytic mechanism are focused on EPR studies of the Mn. We report on a new immobilization strategy linking the enzyme's N-terminal His6-tag to a Zn-loaded immobilized metal affinity resin. Activity is lowered somewhat due to the expected crowding effect. High-field EPR spectra of free and immobilized enzyme show that the resin affects the coordination environment of the active site Mn ions only minimally. The immobilized preparation was used to study the effect of varying pH on the same sample. Repeated freeze-thaw cycles lead to break down of the resin beads and some enzyme loss from the sample. However, the EPR signal increases due to higher packing efficiency on the sample column. Immobilization of Oxalate decarboxylase on Zn-IMAC resin. Overall KM is unaffected after immobilization. Immobilized enzyme exhibits lower overall activity due to crowding on the resin. High-field EPR confirms minimal perturbations of manganese sites due to immobilization.
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Gagnon DM, Brophy MB, Bowman SEJ, Stich TA, Drennan CL, Britt RD, Nolan EM. Manganese binding properties of human calprotectin under conditions of high and low calcium: X-ray crystallographic and advanced electron paramagnetic resonance spectroscopic analysis. J Am Chem Soc 2015; 137:3004-16. [PMID: 25597447 DOI: 10.1021/ja512204s] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Herein, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimer is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin-echo envelope modulation and electron-nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed (15)N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by two to three orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His6 site of human calprotectin.
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Affiliation(s)
- Derek M Gagnon
- Department of Chemistry, University of California , Davis, California 95616, United States
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