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- Title
Conformational dynamics of the tetrameric hemoglobin molecule as revealed by hydrogen exchange: III. The influence of heme removal.
- Authors
Abaturov, L. V.; Nosova, N. G.; Shlyapnikov, S. V.
- Abstract
Two main types of conformational fluctuations, local and global, are characteristic of the native protein structure and are detectable by hydrogen exchange. The probability of such fluctuations changes to a different degree during hemoglobin (Hb) oxygenation, changes in pH, and splitting of the intersubunit contracts. For comparison with the effect of heme removal, the rate of the hydrogen-deuterium (H-D) exchange of peptide H atoms (PHs) of human apoHb was studied by IR spectroscopy at pH 5.5–9.0 and temperatures of 10–38°C. The removal of heme increased the H-D exchange rate for 80% of Hb PHs with the exchange retardation factor P ∼ 102-108. For the majority of PHs, the probability of local fluctuations depended weakly on the temperature; changes in enthalpy upon such local conformational transitions were Δ H = 0–15 kcal/M. Global fluctuations, displaying a stronger temperature dependence, did not arise with an increase in temperature to 38°C at pH 7.0, although apoHb began slowly denaturing and aggregating under these conditions. Destabilization of the apoHb structure with a concurrent decrease in pH to 5.5 and temperature to 10°C intensified global fluctuations in the native protein structure with Δ H < 0. The mechanism underlying the overall intensification of local fluctuations upon the heme removal, the specific features of apoHb heat denaturation under conditions close to those of in vivo Hb self-assembly, and the analogies between low-temperature global fluctuations and cold denaturation of globular proteins are discussed.
- Subjects
HEMOGLOBINS; GLOBULAR proteins; MOLECULAR dynamics; ASPARTATE aminotransferase; INFRARED spectroscopy; MOLECULAR biology; ALCOHOL dehydrogenase
- Publication
Molecular Biology, 2006, Vol 40, Issue 5, p811
- ISSN
0026-8933
- Publication type
Article
- DOI
10.1134/S0026893306050177