Heterogeneity between Two α Subunits of α 2 β 2 Human Hemoglobin and O 2 Binding Properties: Raman, 1 H Nuclear Magnetic Resonance, and Terahertz Spectra

• Published in: Biochemistry (Easton) 2017-11, Vol.56 (46), p.6125-6136
• Main Authors: Nagatomo, Shigenori, Saito, Kazuya, Yamamoto, Kohji, Ogura, Takashi, Kitagawa, Teizo, Nagai, Masako
• Format: Article
• Language: English
• Subjects: Hemoglobin M - chemistry; Hemoglobin M - metabolism; Hemoglobin Subunits - chemistry; Hemoglobin Subunits - metabolism; Hemoglobins, Abnormal - chemistry; Hemoglobins, Abnormal - metabolism; Humans; Models, Molecular; Nuclear Magnetic Resonance, Biomolecular; Oxygen - metabolism; Protein Multimerization; Spectrum Analysis, Raman; Terahertz Spectroscopy
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/acs.biochem.7b00733

Following a previous detailed investigation of the β subunit of α β human adult hemoglobin (Hb A), this study focuses on the α subunit by using three natural valency hybrid α(Fe -deoxy/O )β(Fe ) hemoglobin M (Hb M) in which O cannot bind to the β subunit: Hb M Hyde Park (β92His → Tyr), Hb M Saskatoon (β63His → Tyr), and Hb M Milwaukee (β67Val → Glu). In contrast with the β subunit that exhibited a clear correlation between O affinity and Fe -His stretching frequencies, the Fe -His stretching mode of the α subunit gave two Raman bands only in the T quaternary structure. This means the presence of two tertiary structures in α subunits of the α β tetramer with T structure, and the two structures seemed to be nondynamical as judged from terahertz absorption spectra in the 5-30 cm region of Hb M Milwaukee, α(Fe -deoxy)β(Fe ). This kind of heterogeneity of α subunits was noticed in the reported spectra of a metal hybrid Hb A like α(Fe -deoxy)β(Co ) and, therefore, seems to be universal among α subunits of Hb A. Unexpectedly, the two Fe-His frequencies were hardly changed with a large alteration of O affinity by pH change, suggesting no correlation of frequency with O affinity for the α subunit. Instead, a new Fe -His band corresponding to the R quaternary structure appeared at a higher frequency and was intensified as the O affinity increased. The high-frequency counterpart was also observed for a partially O -bound form, α(Fe -deoxy)α(Fe -O )β(Fe )β(Fe ), of the present Hb M, consistent with our previous finding that binding of O to one α subunit of T structure α β tetramer changes the other α subunit to the R structure.