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Publication Abstract from PubMed

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-A crystal structure of the main hemoglobin component of the Antarctic fish Trematomus newnesi, in a partial hemichrome form. The two alpha-subunit iron atoms are bound to a CO molecule, whereas in the beta 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 beta heme pocket plays a role in the R --> T transition of tetrameric hemoglobins.

The crystal structure of a tetrameric hemoglobin in a partial hemichrome state.,Riccio A, Vitagliano L, di Prisco G, Zagari A, Mazzarella L Proc Natl Acad Sci U S A. 2002 Jul 23;99(15):9801-6. Epub 2002 Jul 1. PMID:12093902^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.