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1cbm

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{{STRUCTURE_1cbm| PDB=1cbm | SCENE= }}
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'''THE 1.8 ANGSTROM STRUCTURE OF CARBONMONOXY-BETA4 HEMOGLOBIN: ANALYSIS OF A HOMOTETRAMER WITH THE R QUATERNARY STRUCTURE OF LIGANDED ALPHA2BETA2 HEMOGLOBIN'''
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===THE 1.8 ANGSTROM STRUCTURE OF CARBONMONOXY-BETA4 HEMOGLOBIN: ANALYSIS OF A HOMOTETRAMER WITH THE R QUATERNARY STRUCTURE OF LIGANDED ALPHA2BETA2 HEMOGLOBIN===
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==Overview==
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The beta-chains isolated from the human hemoglobin alpha 2 beta 2 heterotetramer self-assemble to form a beta 4 homotetramer. We report the structure of the carbonmonoxy-beta 4 (CO beta 4) tetramer refined at a resolution of 1.8 A. Compared to the three known quaternary structures of human hemoglobin, the T state, the R state and the R2 state, the quaternary structure of CO beta 4 most closely resembles the R state. While the degree of structural similarity between CO beta 4 and the R state of liganded alpha 2 beta 2 is quite high, differences between the alpha and beta-chain sequences result in interesting alternative packing arrangements at the subunit interfaces of CO beta 4. In particular, Arg40 beta and Asp99 beta interact across the CO beta 4 equivalent of the alpha 1 beta 2 interface to form two symmetry-related salt bridges that have no counterpart in either liganded or deoxyhemoglobin. Because these salt bridges are near a 2-fold symmetry axis, steric constraints prevent their simultaneous formation, and electron density images of Arg40 beta and Asp99 beta show equally populated dual conformations for the side-chains of both residues. Relative to the liganded alpha 2 beta 2 tetramer, the Arg40 beta...Asp99 beta salt bridges introduce ionic interactions that should strengthen the CO beta 4 tetramer. The CO beta 4 equivalent of the alpha 1 alpha 2 and beta 1 beta 2 interfaces strengthens the tetramer relative to the liganded alpha 2 beta 2 tetramer by tethering both ends of the central cavity. (The entrance to the central cavity is altered so that the N termini move closer together and the C termini further apart, forming an anion binding pocket that is absent in liganded alpha 2 beta 2 hemoglobin.) In contrast, analysis of the CO beta 4 counterpart of the alpha 1 beta 1 interface indicates that this interface is weakened in the CO beta 4 tetramer. These differences in interface stability provide a structural explanation for the published observation that the alpha 2 beta 2 tetramer assembles via a stable alpha 1 beta 1 dimer intermediate, whereas assembly of the CO beta 4 tetramer is characterized more accurately by a monomer-tetramer equilibrium.
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{{ABSTRACT_PUBMED_8114096}}
==About this Structure==
==About this Structure==
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[[Category: Borgstahl, G E.O.]]
[[Category: Borgstahl, G E.O.]]
[[Category: Oxygen transport]]
[[Category: Oxygen transport]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 12:33:22 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 20:31:06 2008''

Revision as of 17:31, 30 June 2008

Image:1cbm.png

Template:STRUCTURE 1cbm

THE 1.8 ANGSTROM STRUCTURE OF CARBONMONOXY-BETA4 HEMOGLOBIN: ANALYSIS OF A HOMOTETRAMER WITH THE R QUATERNARY STRUCTURE OF LIGANDED ALPHA2BETA2 HEMOGLOBIN

Template:ABSTRACT PUBMED 8114096

About this Structure

1CBM is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.

Reference

The 1.8 A structure of carbonmonoxy-beta 4 hemoglobin. Analysis of a homotetramer with the R quaternary structure of liganded alpha 2 beta 2 hemoglobin., Borgstahl GE, Rogers PH, Arnone A, J Mol Biol. 1994 Feb 25;236(3):817-30. PMID:8114096

Page seeded by OCA on Mon Jun 30 20:31:06 2008

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