Keywords: Antarctic, Protein Denaturation, Protein Function, X-Ray Structure, Hemoglobin, Tetramer, Article, Complex Formation, Crystal Structure, Crystallization, Heme Synthesis, Hemoglobin Synthesis, Ligand Binding, Nonhuman, Plasticity, Priority Journal, Protein Folding, Protein Quaternary Structure, Structure Analysis, Amino Acid Sequence, Animals, Antarctic Regions, Crystallography, Fishes, Models, Molecular, Protein Structure, Secondary, Protein Subunits, Trematomus, Trematomus Newnesi,
Affiliations: *** IBB - CNR ***
Istituto di Biochimica delle Proteine ed Enzimologia, Consiglio Nazionale delle Ricerche, I-80125 Naples, Italy
Istituto di Biostrutture e Bioimmagini, Consiglio Nazionale delle Ricerche, I-80134 Naples, Italy
Dipartimento di Chimica Biologica, Università degli Studi di Napoli Federico II, I-80134 Naples, Italy
Centro di Ingegneria Genetica, Biotecnologie Avanzate SCARL, I-80131 Naples, Italy
References: Not available.
The crystal structure of a tetrameric hemoglobin in a partial hemichrome state
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-Angstrom 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