Cold-Adaptation Signatures in the Ligand Rebinding Kinetics to the Truncated Hemoglobin of the Antarctic Bacterium Pseudoalteromonas haloplanktis TAC125

Cold-adapted organisms have evolved proteins endowed with higher flexibility and lower stability in comparison to their thermophilic homologs, resulting in enhanced reaction rates at low temperatures. In this context, protein-bound water molecules were suggested to play a major role, and their weaker interactions at protein active sites has been associated to cold adaptation. In this work, we tested this hypothesis on truncated hemoglobins - a family of microbial heme-proteins of yet-unclear function - applying Molecular-Dynamics simulations and ligand-rebinding kinetics on a protein from the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 in comparison with its thermophilic Thermobifida fusca homologue. The CO rebinding kinetics of the former highlight several geminate phases, with an unusually long lived geminate intermediate. An articulated tunnel with at least two distinct docking sites was ...