1ns9: Difference between revisions

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The 1.6A Structure of Horse Methemoglobin at pH 7.1

OverviewOverview

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.

About this StructureAbout this Structure

1NS9 is a Protein complex structure of sequences from Equus caballus with as ligand. Full crystallographic information is available from OCA.

ReferenceReference

A pH-dependent aquomet-to-hemichrome transition in crystalline horse methemoglobin., Robinson VL, Smith BB, Arnone A, Biochemistry. 2003 Sep 2;42(34):10113-25. PMID:12939139

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 caption="1ns9, resolution 1.60&Aring;" />
 '''The 1.6A Structure of Horse Methemoglobin at pH 7.1'''<br />
 ==Overview==
-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.
+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.
 ==About this Structure==
-NS9 is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Equus_caballus Equus caballus] with HEM as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1NS9 OCA].
+NS9 is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Equus_caballus Equus caballus] with <scene name='pdbligand=HEM:'>HEM</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1NS9 OCA].
 ==Reference==
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 [[Category: Protein complex]]
 [[Category: Arnone, A.]]
-[[Category: Robinson, V.L.]]
+[[Category: Robinson, V L.]]
-[[Category: Smith, B.B.]]
+[[Category: Smith, B B.]]
 [[Category: HEM]]
 [[Category: aquomet hemoglobin]]
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 [[Category: globin fold]]
-''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Thu Nov  8 13:14:16 2007''
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