Hierarchic Assemblies Control the Active Site Structure in Giant Bilayer Hemoglobin From the Annelid Eisenia foetida

The active site structure of the oxygenated derivative of the main subassemblies (whole protein, dodecamers and trimers) of the giant haemoglobin from Eisenia foetida has been characterized by X-ray Absorption Near Edge Structure (XANES) spectroscopy. The data revealed a remarkable effect of the hierarchic assemblies on the active site of the subunit. Specifically, the whole protein has the same site structure of the dodecamer, while a sharp conformational transition occurs when the dodecamer is disassembled into trimers (and monomers) revealing that constraints due to the protein matrix determine the active site geometry and, consequently, the protein function in these large complexes.