Myoglobin-Membrane Association Facilitates Oxygen Release via Active-Site Tuning

Myoglobin, a heme protein abundant in striated muscle cells, plays a crucial role in oxygen delivery to mitochondria. In this study, we combined spectroscopy, rapid kinetics and computer simulations to investigate how the interaction between oxymyoglobin and an outer mitochondrial membrane model - composed of 1:1 POPC:POPE liposomes- impacts oxygen affinity. UV-visible and Resonance Raman spectroscopy studies of metmyoglobin, deoxymyoglobin and oxymyoglobin reveal subtle structural perturbations of the heme binding site, when oxymyoglobin interacts with the model membrane. Stopped-flow kinetic measurements show that these distortions lead to a 2-fold increase in the rate constant for oxygen release. Furthermore, classical and multiscale QM/MM simulations suggest that the increase in the O₂ dissociation rate in the presence of the liposomes is mainly due to proximal effects and heme plane distortions produced by specific interactions between oxymyoglobin and the membrane. Altogether, these results point to a fine-tuning in the active site conformation that facilitates oxygen release from oxymyoglobin upon membrane association, potentially enhancing mitochondrial oxygen availability and energy production in cells.