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A role of heme side-chains of human hemoglobin in its function revealed by circular dichroism and resonance Raman

Masako Nagai1,2, Naoki Mizusawa3, Teizo Kitagawa4

  • 1Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, 184-0003, Japan. masako.nagai.34@hosei.ac.jp.

Biophysical Reviews
|December 21, 2017
PubMed

Structural changes of heme side-chains of human adult hemoglobin (Hb A) upon ligand (O2 or CO) dissociation have been studied by circular dichroism (CD) and resonance Raman (RR) spectroscopies. We point out the occurrence of appreciable deformation of heme side-chains like vinyl and propionate groups prior to the out-of-plane displacement of heme iron. Referring to the recent fine resolved crystal structure of Hb A, the deformations of heme side-chains take place only in the β subunits. However, these changes are not observed in the isolated β chain (β4 homotetramer) and, therefore, are associated with the α-β inter-subunit interactions. For the communications between α and β subunits in Hb A regarding signals of ligand dissociation, possible routes are proposed on the basis of the time-resolved absorption, CD, MCD (magnetic CD), and RR spectroscopies. Our finding of the movements of heme side-chains would serve as one of the clues to solve the cooperative O2 binding mechanism of Hb A.

Keywords:
Circular dichroismCooperative oxygen bindingDeformations of heme side-chainsHuman hemoglobinResonance RamanSubunits interactions

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