Nagai Masako, Mizusawa Naoki, Kitagawa Teizo, Nagatomo Shigenori
Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, 184-0003, Japan.
School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Ishikawa, 920-0942, Japan.
Biophys Rev. 2018 Apr;10(2):271-284. doi: 10.1007/s12551-017-0364-5. Epub 2017 Dec 19.
Structural changes of heme side-chains of human adult hemoglobin (Hb A) upon ligand (O 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 (β 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 O binding mechanism of Hb A.
通过圆二色光谱（CD）和共振拉曼光谱（RR）研究了成人血红蛋白（Hb A）配体（O或CO）解离时血红素侧链的结构变化。我们指出，在血红素铁发生平面外位移之前，乙烯基和丙酸根基团等血红素侧链会发生明显变形。参照最近高分辨率的Hb A晶体结构，血红素侧链的变形仅发生在β亚基中。然而，在分离的β链（β同四聚体）中未观察到这些变化，因此，这些变化与α-β亚基间相互作用有关。基于时间分辨吸收光谱、CD光谱、磁圆二色光谱（MCD）和RR光谱，提出了Hb A中α和β亚基之间关于配体解离信号的可能传递途径。我们对血红素侧链运动的发现将作为解决Hb A协同氧结合机制的线索之一。
