Protonation of Histidine 55 affects the oxygen access to heme in the alpha chain of the hemoglobin from the Antarctic fish Trematomus bernacchii

BOECHI, L.; MARTI, M.A.; VERGARA, A.; SICA, F.; MAZZARELLA, L.; ESTRIN, D.A.; MERLINO, A.

IUBMB LIFE

JOHN WILEY & SONS INC

Lugar: Malden; Año: 2011 vol. 63 p. 175 - 182

1521-6543

SummaryThe Root effect describes the drastic drop of oxygen affinityand loss of cooperativity at acidic pH expressed in the hemoglo-bins (Hb) of certain fish. The comparison between the deoxystructures of the Root effect Hb from the Antarctic fish Trema-tomus bernacchii (HbTb) at different pHs (pH 5 6.2 and pH 58.4) shows that the most significant differences are localized atthe CDa region, where a salt bridge between Asp48 and His55breaks during the low-to-high pH transition. In order to shedlight on the relationship between pH, CDa loop structure anddynamics, and oxygen access to the active site in the alphachain of HbTb, different computer simulation techniques wereperformed. Our results highlight the importance of the protona-tion of His55 in regulating oxygen access, underscoring its piv-otal role in the structural and functional properties of HbTb.These data provide further support to the hypothesis that thisresidue might contribute to the release of Root protons inHbTb and underline the fact that an efficient transport of mo-lecular oxygen in Hbs relies on a subtle balance of tertiarystructure and protein conformational flexibility.