X-ray diffraction studies of a partially liganded hemoglobin, [α(FeII-CO)β(MnII)]2

Arthur Arnone*, Paul Rogers, Neil V. Blough, Jacqueline L. McGourty, Brian M. Hoffman

*Corresponding author for this work

Research output: Contribution to journalArticle

50 Scopus citations

Abstract

We have applied single-crystal X-ray diffraction methods to analyze the structure of [α(FeII-CO)β(MnII)]2, a mixed-metal hybrid hemoglobin that crystallizes in the deoxyhemoglobin quaternary structure (the T-state) even though it is half liganded. This study, carried out at a resolution of 3·0 Å, shows that (1) the Mn(II)-substituted β subunits are structurally isomorphous with normal deoxy β subunits, and (2) CO binding to the α subunits induces small, localized changes in the T-state that lack the main directional component of the corresponding larger structural changes in subunit tertiary structure that accompany complete ligand binding to all four subunits and the deoxy to oxy quaternary structure change. Specifically, in the T-state, CO binding to the α heme group draws the iron atom toward the heme plane, and this in turn pulls the last turn of the F helix (residues 85 through 89) closer to the heme group. The direction of these small movements is almost perpendicular to the axis of the F helix. In contrast, when the structures of fully liganded and deoxyhemoglobin are compared, extensive structural changes occur throughout the F helix and FG corner, and the main component of the atomic movements in the F helix (in addition to the smaller component toward the heme) is in a direction parallel to the heme plane and toward the α1β2 interface. These findings are discussed in terms of the current stereochemical theories of co-operative ligand binding and the Bohr effect.

Original languageEnglish (US)
Pages (from-to)693-706
Number of pages14
JournalJournal of Molecular Biology
Volume188
Issue number4
DOIs
StatePublished - Apr 20 1986

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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