Fig. 1: Different myoglobin variants examined in this work.

a The crystal structure of the Leu29Phe mutant of Physeter macrocephalus myoglobin (High affinity whale Mb, PDB ID: 2SPL58), showing that Phe29 stabilises His64 in a conformation where it can coordinate the bound ligand (in this case CO). b The structure of wild-type Physeter macrocephalus myoglobin (Sperm whale Mb, PDB ID: 1VXC59). c The crystal structure of the His64Leu mutant of Physeter macrocephalus myoglobin (Low affinity whale Mb, PDB ID: 2MGE32), showing that the Leu64 mutation removes the ligand-coordinating imidazole sidechain of His64. The electrostatic surface of Physeter macrocephalus myoglobin (Sperm whale Mb) (d) and Equus caballas myoglobin (Horse Mb)(1AZI60) (e), showing the greater cationic (blue) surface charge and pI of Physeter macrocephalus myoglobin.