A pH-dependent aquomet-to-hemichrome transition in crystalline horse methemoglobin.
Abstract: In 1947, Perutz and co-workers reported that crystalline horse methemoglobin undergoes a large lattice transition as the pH is decreased from 7.1 to 5.4. We have determined the pH 7.1 and 5.4 crystal structures of horse methemoglobin at 1.6 and 2.1 A resolution, respectively, and find that this lattice transition involves a 23 A translation of adjacent hemoglobin tetramers as well as changes in alpha heme ligation and the tertiary structure of the alpha subunits. Specifically, when the pH is lowered from 7.1 to 5.4, the Fe(3+) alpha heme groups (but not the beta heme groups) are converted from the aquomet form, in which the proximal histidine [His87(F8)alpha] and a water molecule are the axial heme ligands, to the hemichrome (bishistidine) form, in which the proximal histidine and the distal histidine [His58(E7)alpha] are the axial heme ligands. Hemichrome formation is coupled to a large tertiary structure transition in the eight-residue segment Pro44(CD2)alpha-Gly51(D7)alpha that converts from an extended loop structure at pH 7.1 to a pi-like helix at pH 5.4. The formation of the pi helix forces Phe46(CD4)alpha out of the alpha heme pocket and into the interface between adjacent hemoglobin tetramers where it participates in crystal lattice contacts unique to the pH 5.4 structure. In addition, the transition from aquomet alpha subunits to bishistidine alpha subunits is accompanied by an approximately 1.2 A movement of the alpha heme groups to a more solvent-exposed position as well as the creation of a solvent channel from the interior of the alpha heme pocket to the outside of the tetramer. These changes and the extensive rearrangement of the crystal lattice structure allow the alpha heme group of one tetramer to make direct contact with an alpha heme group on an adjacent tetramer. These results suggest possible functional roles for hemichrome formation in vivo.
Publication Date: 2003-08-27 PubMed ID: 12939139DOI: 10.1021/bi030059tGoogle Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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The research paper discusses the pH-dependent change in the structure of horse methemoglobin from aquomet to hemichrome form when the pH is reduced from 7.1 to 5.4.
Research Method and Findings
The research was carried out based on an earlier study reported by Perutz and his team in 1947. This initial research showed that crystalline horse methemoglobin experienced significant changes in its lattice structure when the pH was reduced from 7.1 to 5.4. In the current research, the molecular structures at these two pH levels were determined – at a resolution of 1.6 and 2.1 A respectively – discovering that:
- The lattice transition involves a 23 A translation of adjacent hemoglobin tetramers, changes in alpha heme ligation, and alterations in the tertiary structure of the alpha subunits.
The researchers found that when the pH is lowered from 7.1 to 5.4:
- The Fe(3+) alpha heme groups, but not the beta heme groups, are converted from an aquomet form, where the axial heme ligands are the proximal histidine and water molecule, to a hemichrome form with the axial heme ligands being the proximal and distal histidine.
- Hemichrome creation is associated with a significant tertiary structure transition in the eight-residue segment that transitions from an extended loop structure at pH 7.1 to a pi-like helix at pH 5.4.
- The creation of the pi-helix forces Phe46(CD4)alpha out of the alpha heme pocket and into the interface amid adjacent hemoglobin tetramers, where it participates in crystal lattice contacts unique to the pH 5.4 structure.
- The transition from aquomet alpha subunits to bishistidine alpha subunits involves an approximately 1.2 A movement of the alpha heme groups to a more solvent-exposed position as well as the creation of a solvent channel from the interior of the alpha heme pocket to the outside of the tetramer.
Implication of Findings
The changes and the extensive rearrangement of the crystal lattice structure allow an alpha heme group of one tetramer to make direct contact with an alpha heme group on an adjacent tetramer. This suggests potential functional roles for hemichrome formation in natural biological processes.
Cite This Article
APA
Robinson VL, Smith BB, Arnone A.
(2003).
A pH-dependent aquomet-to-hemichrome transition in crystalline horse methemoglobin.
Biochemistry, 42(34), 10113-10125.
https://doi.org/10.1021/bi030059t Publication
Researcher Affiliations
- Department of Biochemistry, College of Medicine, The University of Iowa, Iowa City, Iowa 52242, USA.
MeSH Terms
- Animals
- Crystallography, X-Ray
- Dimerization
- Ferric Compounds / chemistry
- Heme / chemistry
- Hemeproteins / chemistry
- Histidine / chemistry
- Horses
- Hydrogen Bonding
- Hydrogen-Ion Concentration
- Ligands
- Methemoglobin / chemistry
- Models, Molecular
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Protein Subunits / chemistry
- Static Electricity
- Water / chemistry
Grant Funding
- GM-58890 / NIGMS NIH HHS
Citations
This article has been cited 16 times.- Powell SM, Wang B, Herrera VE, Prather KY, Nguyen NT, Abucayon EG, Thomas LM, Safo MK, Richter-Addo GB. Crystal structural investigations of heme protein derivatives resulting from reactions of aryl- and alkylhydroxylamines with human hemoglobin.. J Inorg Biochem 2023 Sep;246:112304.
- De Simone G, di Masi A, Tundo GR, Coletta M, Ascenzi P. Nitrite Reductase Activity of Ferrous Nitrobindins: A Comparative Study.. Int J Mol Sci 2023 Mar 31;24(7).
- Ioannou A, Varotsis C. Probing hemoglobin glyco-products by fluorescence spectroscopy.. RSC Adv 2019 Nov 13;9(64):37614-37619.
- Lecomte JTJ. Hemoglobin: Some (Dis)Assembly Required.. Biophys J 2020 Mar 24;118(6):1235-1237.
- Balasco N, Vitagliano L, Merlino A, Verde C, Mazzarella L, Vergara A. The unique structural features of carbonmonoxy hemoglobin from the sub-Antarctic fish Eleginops maclovinus.. Sci Rep 2019 Dec 12;9(1):18987.
- Ioannou A, Varotsis C. Modifications of hemoglobin and myoglobin by Maillard reaction products (MRPs).. PLoS One 2017;12(11):e0188095.
- Bowden CFM, Chan ACK, Li EJW, Arrieta AL, Eltis LD, Murphy MEP. Structure-function analyses reveal key features in Staphylococcus aureus IsdB-associated unfolding of the heme-binding pocket of human hemoglobin.. J Biol Chem 2018 Jan 5;293(1):177-190.
- Mohamed Abubakkar M, Saraboji K, Ponnuswamy MN. Purification, crystallization and preliminary crystallographic studies of haemoglobin from mongoose (Helogale parvula) in two different crystal forms induced by pH variation.. Acta Crystallogr Sect F Struct Biol Cryst Commun 2013 Feb 1;69(Pt 2):126-9.
- Yi J, Thomas LM, Musayev FN, Safo MK, Richter-Addo GB. Crystallographic trapping of heme loss intermediates during the nitrite-induced degradation of human hemoglobin.. Biochemistry 2011 Oct 4;50(39):8323-32.
- Yi J, Thomas LM, Richter-Addo GB. Structure of human R-state aquomethemoglobin at 2.0 Å resolution.. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011 Jun 1;67(Pt 6):647-51.
- Kakar S, Hoffman FG, Storz JF, Fabian M, Hargrove MS. Structure and reactivity of hexacoordinate hemoglobins.. Biophys Chem 2010 Nov;152(1-3):1-14.
- Nieves-Marrero CA, Ruiz-Martínez CR, Estremera-Andújar RA, González-Ramírez LA, López-Garriga J, Gavira JA. Two-step counterdiffusion protocol for the crystallization of haemoglobin II from Lucina pectinata in the pH range 4-9.. Acta Crystallogr Sect F Struct Biol Cryst Commun 2010 Mar 1;66(Pt 3):264-8.
- Gell DA, Feng L, Zhou S, Jeffrey PD, Bendak K, Gow A, Weiss MJ, Shi Y, Mackay JP. A cis-proline in alpha-hemoglobin stabilizing protein directs the structural reorganization of alpha-hemoglobin.. J Biol Chem 2009 Oct 23;284(43):29462-9.
- Hong X, Hao Q. Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites.. J Appl Crystallogr 2009 Apr 1;42(Pt 2):259-264.
- Vergara A, Franzese M, Merlino A, Vitagliano L, Verde C, di Prisco G, Lee HC, Peisach J, Mazzarella L. Structural characterization of ferric hemoglobins from three antarctic fish species of the suborder notothenioidei.. Biophys J 2007 Oct 15;93(8):2822-9.
- Verde C, Howes BD, De Rosa MC, Raiola L, Smulevich G, Williams R, Giardina B, Parisi E, Di Prisco G. Structure and function of the Gondwanian hemoglobin of Pseudaphritis urvillii, a primitive notothenioid fish of temperate latitudes.. Protein Sci 2004 Oct;13(10):2766-81.
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