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1sct

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(New page: 200px<br /> <applet load="1sct" size="450" color="white" frame="true" align="right" spinBox="true" caption="1sct, resolution 2.0Å" /> '''SCAPHARCA TETRAMERIC...)
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Revision as of 11:11, 8 November 2007

Image:1sct.gif

SCAPHARCA TETRAMERIC HEMOGLOBIN, CO-STATE

Overview

The crystal structure of the allosteric tetrameric hemoglobin from, Scapharca inaequivalvis (HbII) has been determined in the carbonmonoxy, liganded state using a combination of anomalous scattering and molecular, replacement. The molecular model has been refined at 2.0 A resolution to a, conventional R-factor of 0.173 and a free R-factor of 0.244. The tetramer, is formed from two identical heterodimers. Each heterodimer is assembled, with intersubunit contacts involving the E and F helices and heme groups, in a manner that is very similar to that of the cooperative Scapharca, homodimeric hemoglobin. In addition, the ordered water structure observed, in these dimeric interfaces is quite similar. These structural, similarities strongly suggest that the dimers within the Scapharca, tetramer are cooperative. Subunits assemble into a tetramer in a, distinctly non-tetrahedral arrangement, with the pseudo 2-fold axes of the, heterodimer oriented at an angle of 74.5 degrees relative to the molecular, 2-fold. This arrangement requires that two subunit types have distinct, locations and contacts, despite the very similar tertiary structures. HbII, polymerizes to higher-order assemblages in a ligand, proton and anion, dependent fashion. The lattice contacts in the HbII-CO crystal suggest, possible modes for this association.

About this Structure

1SCT is a Protein complex structure of sequences from Scapharca inaequivalvis with ACE, HEM and CMO as ligands. Full crystallographic information is available from OCA.

Reference

The 2.0 A crystal structure of Scapharca tetrameric hemoglobin: cooperative dimers within an allosteric tetramer., Royer WE Jr, Heard KS, Harrington DJ, Chiancone E, J Mol Biol. 1995 Oct 13;253(1):168-86. PMID:7473710

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