Heme-bound tyrosine vibrations in hemoglobin M: Resonance Raman, crystallography, and DFT calculation

Hemoglobins M (Hbs M) are human hemoglobin variants in which either the α or β subunit contains a ferric heme in the α2β2 tetramer. Though the ferric subunit cannot bind O2, it regulates O2 affinity of its counterpart ferrous subunit. We have investigated resonance Raman spectra of two Hbs, M Iwate...

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Published in:Biophysical journal 2022-07, Vol.121 (14), p.2767-2780
Main Authors: Nagatomo, Shigenori, Shoji, Mitsuo, Terada, Takuto, Nakatani, Kiyoharu, Shigeta, Yasuteru, Hirota, Shun, Yanagisawa, Sachiko, Kubo, Minoru, Kitagawa, Teizo, Nagai, Masako, Ohki, Mio, Park, Sam-Yong, Shibayama, Naoya
Format: Article
Language:English
Subjects:
Crystallography
Density Functional Theory
Heme - chemistry
Hemoglobin M - chemistry
Hemoglobin M - metabolism
Humans
Spectrum Analysis, Raman
Tyrosine - chemistry
Vibration
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Summary:Hemoglobins M (Hbs M) are human hemoglobin variants in which either the α or β subunit contains a ferric heme in the α2β2 tetramer. Though the ferric subunit cannot bind O2, it regulates O2 affinity of its counterpart ferrous subunit. We have investigated resonance Raman spectra of two Hbs, M Iwate (α87His → tyrosine [Tyr]) and M Boston (α58His → Tyr), having tyrosine as a heme axial ligand at proximal and distal positions, respectively, that exhibit unassigned resonance Raman bands arising from ferric (not ferrous) hemes at 899 and 876 cm-1. Our quantum chemical calculations using density functional theory on Fe-porphyrin models with p-cresol and/or 4-methylimidazole showed that the unassigned bands correspond to the breathing-like modes of Fe3+-bound Tyr and are sensitive to the Fe-O-C(Tyr) angle. Based on the frequencies of the Raman bands, the Fe-O-C(Tyr) angles of Hbs M Iwate and M Boston were predicted to be 153.5° and 129.2°, respectively. Consistent with this prediction, x-ray crystallographic analysis showed that the Fe-O-C(Tyr) angles of Hbs M Iwate and M Boston in the T quaternary structure were 153.6° and 134.6°, respectively. It also showed a similar Fe-O bond length (1.96 and 1.97 Å) and different tilting angles. [Display omitted]
ISSN:0006-3495
1542-0086
DOI:10.1016/j.bpj.2022.06.012