Exploring Compactness and Dynamics of Apomyoglobin

Hydrogen-deuterium exchange mass spectrometry (HDX-MS) approach has become a valuable analytical complement to traditional methods. HDX-MS allows the identification of dynamic surfaces in proteins. We have shown that the introduction of various mutations into the amino acid sequence of whale apomyoglobin (apoMb) leads to a change in the number of exchangeable hydrogen atoms, which is associated with a change in its compactness in the native-like condition. Thus, amino acid substitutions V10A, A15S, P120G, and M131A result in an increase in the number of exchangeable hydrogen atoms at the native-like condition, while the mutant form A144S leads to a decrease in the number of exchangeable hydrogen atoms. This may be due to a decrease and increase in the compactness of apoMb structure compared to the wild-type apoMb, respectively. The L9F and L9E mutations did not affect the compactness of the molecule compared to the wild type. We have demonstrated that V10A and M131A substitutions lead to the maximum and large increase correspondently in the average number of exchangeable hydrogen atoms for deuterium, since these substitutions lead to the loss of contacts between important parts of myoglobin structure: helices A, G, and H, which are structured at the early stage of folding.