A New Way To Understand Quaternary Structure Changes of Hemoglobin upon Ligand Binding On the Basis of UV-Resonance Raman Evaluation of Intersubunit Interactions
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- 作者：Shigenori Nagatomo ; Masako Nagai ; Teizo Kitagawa
- 刊名：Journal of the American Chemical Society
- 出版年：2011
- 出版时间：July 6, 2011
- 年：2011
- 卷：133
- 期：26
- 页码：10101-10110
- 全文大小：1144K
- 年卷期：v.133,no.26(July 6, 2011)
- ISSN：1520-5126
文摘
The single residue vibrational spectra of tryptophan (Trp) and tyrosine (Tyr) residues in human adult hemoglobin (HbA), which play important roles in cooperative oxygen binding, were determined for the deoxy and CO-bound forms by applying UV resonance Raman spectroscopy to various variant Hbs. It was found that Trp尾37, Tyr伪42, Tyr伪140, and Tyr尾145 at the 伪1鈥撐?sup>2 subunit interface underwent transitions between two contact states (named as T and R) upon ligand binding, while Trp伪14, Trp尾15, and Tyr尾35 displayed little changes. The corresponding spectral changes were identified only for the 伪2尾2 tetramer, but not the isolated 伪 and 尾 chains in the oligomeric forms, and therefore were exclusively attributed to a quaternary structure change. Ligand binding as well as allosteric effectors and pH altered only the number of the T-contacted Tyr and Trp residues without varying the two contact states themselves. A new method to semiquantitatively evaluate the amount of T-contacted Tyr and Trp residues in a given liganded form is here proposed, and with it a quaternary structure was determined for various symmetrically half-liganded forms obtained with ligand鈥揾ybrid, metal鈥揾ybrid, and valency鈥揾ybrid Hbs. It was found that ligand binding to the 伪 or 尾 subunits yielded different subunit contacts and that the contact changes of the Trp and Tyr residues were not always concerted. The contact changes at the 伪1鈥撐?sup>2 (伪2鈥撐?sup>1) interface are correlated with the proximal strain exerted on the Fe鈥揌is(F8) bond, which is noted to be much larger in the 伪 than 尾 subunits in the 伪2尾2 tetramer.