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The crystal structure of a tetrameric hemoglobin in a partial hemichrome state

By Antonio Riccio, Luigi Vitagliano, Guido di Prisco, Adriana Zagari and Lelio Mazzarella

Abstract

Tetrameric hemoglobins are the most widely used systems in studying protein cooperativity. Allosteric effects in hemoglobins arise from the switch between a relaxed (R) state and a tense (T) state occurring upon oxygen release. Here we report the 2.0-Å crystal structure of the main hemoglobin component of the Antarctic fish Trematomus newnesi, in a partial hemichrome form. The two α-subunit iron atoms are bound to a CO molecule, whereas in the β subunits the distal histidine residue is the sixth ligand of the heme iron. This structure, a tetrameric hemoglobin in the hemichrome state, demonstrates that the iron coordination by the distal histidine, usually associated with denaturing states, may be tolerated in a native-like hemoglobin structure. In addition, several features of the tertiary and quaternary organization of this structure are intermediate between the R and T states and agree well with the R → T transition state properties obtained by spectroscopic and kinetic techniques. The analysis of this structure provides a detailed pathway of heme–heme communication and it indicates that the plasticity of the β heme pocket plays a role in the R → T transition of tetrameric hemoglobins

Topics: Biological Sciences
Publisher: The National Academy of Sciences
Year: 2002
DOI identifier: 10.1073/pnas.132182099
OAI identifier: oai:pubmedcentral.nih.gov:125021
Provided by: PubMed Central
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