1NS6

The 2.1A Structure of Horse (alpha hemichrome/beta met) Hemoglobin at pH 5.4

1NS6 の概要

• エントリーDOI: 10.2210/pdb1ns6/pdb
• 関連するPDBエントリー: 1NS9
• 分子名称: Hemoglobin alpha subunit, Hemoglobin beta subunit, PROTOPORPHYRIN IX CONTAINING FE, ... (4 entities in total)
• 機能のキーワード: hemichrome, bisimidazole alpha heme, aquomet beta heme, globin fold, oxygen storage-transport complex, oxygen storage/transport
• 由来する生物種: Equus caballus (horse); 詳細
• タンパク質・核酸の鎖数: 2
• 化学式量合計: 32403.53

構造登録者

Robinson, V.L.,Smith, B.B.,Arnone, A. (登録日: 2003-01-27, 公開日: 2003-10-14, 最終更新日: 2023-08-16)

主引用文献

Robinson, V.L.,Smith, B.B.,Arnone, A.
A pH-Dependent Aquomet-to-Hemichrome Transition in Crystalline Horse Methemoglobin
Biochemistry, 42:10113-10125, 2003

PubMed 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.

PubMed: 12939139
DOI: 10.1021/bi030059t

実験手法

X-RAY DIFFRACTION (2.05 Å)