EXAFS Comparison of the Dimanganese Core Structures of Manganese Catalase, Arginase, and Manganese-Substituted Ribonucleotide Reductase and Hemerythrin
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- 作者：Timothy L. Stemmler ; Thomas M. Sossong ; Jr. ; Jonathan I. Goldstein ; David E. Ash ; Timothy E. Elgren ; Donald M. Kurtz ; Jr. ; and James E. Penner-Hahn
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：August 12, 1997
- 年：1997
- 卷：36
- 期：32
- 页码：9847 - 9858
- 全文大小：371K
- 年卷期：v.36,no.32(August 12, 1997)
- ISSN：1520-4995
文摘
The solution structures of the binuclear Mn centers in arginase,Mn catalase, and the Mn-substituted forms of the Fe enzymes ribonucleotide reductase andhemerythrin have been determinedusing X-ray absorption spectroscopy (XAS). X-ray absorption nearedge structure (XANES) spectra forthese proteins were compared to those obtained for Mn(II) models.The Mn model spectra show aninverse correlation between the XANES peak maximum and theroot-mean-square (RMS) deviation inmetal-ligand bond lengths. For these complexes, the XANES maximaappear to be more effective thanthe 1s 
3d areas as an indicator of metal-site symmetry.Arginase and Mn-substituted ribonucleotidereductase have symmetric nearest neighbor environments with low RMSdeviation in bond length, whileMn catalase and Mn-substituted hemerythrin appear to have a larger RMSbond length deviation. The 1s 3d areas for arginase and Mn-substituted ribonucleotide reductaseare consistent with six coordinateMn, while the 1s 3d areas for Mn catalase and Mn-substitutedhemerythrin are larger, suggesting thatone or both of the Mn ions are five-coordinate in these proteins.Extended x-ray absorption fine structure(EXAFS) spectra were used to determine the Mn2 corestructure for the four proteins. In order toquantitatethe number of histidine residues bound to the Mn2 centers,EXAFS data for the crystallographicallycharacterized model hexakis-imidazole Mn(II) dichloridetetrahydrate were used to calibrate the Mn-imidazole multiple scattering interactions. These calibratedparameters allowed the outer shell EXAFSto be fit to give a lower limit on the number of bound histidineresidues. The EXAFS spectra for Mn-substituted ribonucleotide reductase and arginase are nearly identical,with symmetric Mn-nearest neighborenvironments and outer shell scattering consistent with a lower limitof one histidine per Mn2 core. Incontrast, the EXAFS data for Mn catalase and Mn-substituted hemerythrinshow two distinct Mn-nearestneighbor shells, modeled as Mn-O at ca. 2.1 Å and Mn-N at ca. 2.3Å, and outer shell carbon scatteringconsistent with a lower limit of ca. 2-3 His residues perMn2 core. Only Mn catalase shows clearevidencefor Mn···Mn scattering. The observed Mn···Mndistance is 3.53 Å, which is significantly longer thanthe ~3.3 Å distances that are typically observed forMn(II)2 cores with two single atom bridges,butwhich is typical of the distances seen in Mn(II)2cores having one single atom bridge (e.g., aqua orhydroxo)together with one or two carboxylate bridges. The absence ofEXAFS-detectable Mn···Mn interactionsfor the other three proteins suggests either that there are no singleatom bridges in these cases or that theMn···Mn interactions are more disordered.
3d areas as an indicator of metal-site symmetry.Arginase and Mn-substituted ribonucleotidereductase have symmetric nearest neighbor environments with low RMSdeviation in bond length, whileMn catalase and Mn-substituted hemerythrin appear to have a larger RMSbond length deviation. The 1s 3d areas for arginase and Mn-substituted ribonucleotide reductaseare consistent with six coordinateMn, while the 1s 3d areas for Mn catalase and Mn-substitutedhemerythrin are larger, suggesting thatone or both of the Mn ions are five-coordinate in these proteins.Extended x-ray absorption fine structure(EXAFS) spectra were used to determine the Mn2 corestructure for the four proteins. In order toquantitatethe number of histidine residues bound to the Mn2 centers,EXAFS data for the crystallographicallycharacterized model hexakis-imidazole Mn(II) dichloridetetrahydrate were used to calibrate the Mn-imidazole multiple scattering interactions. These calibratedparameters allowed the outer shell EXAFSto be fit to give a lower limit on the number of bound histidineresidues. The EXAFS spectra for Mn-substituted ribonucleotide reductase and arginase are nearly identical,with symmetric Mn-nearest neighborenvironments and outer shell scattering consistent with a lower limitof one histidine per Mn2 core. Incontrast, the EXAFS data for Mn catalase and Mn-substituted hemerythrinshow two distinct Mn-nearestneighbor shells, modeled as Mn-O at ca. 2.1 Å and Mn-N at ca. 2.3Å, and outer shell carbon scatteringconsistent with a lower limit of ca. 2-3 His residues perMn2 core. Only Mn catalase shows clearevidencefor Mn···Mn scattering. The observed Mn···Mndistance is 3.53 Å, which is significantly longer thanthe ~3.3 Å distances that are typically observed forMn(II)2 cores with two single atom bridges,butwhich is typical of the distances seen in Mn(II)2cores having one single atom bridge (e.g., aqua orhydroxo)together with one or two carboxylate bridges. The absence ofEXAFS-detectable Mn···Mn interactionsfor the other three proteins suggests either that there are no singleatom bridges in these cases or that theMn···Mn interactions are more disordered.