Control of active site structure of giant bilayer hemoglobin from the annellid Eisenia foetida using hierarchic assemblies

The active site structure of the oxygenated derivative of the main subassemblies ͑whole protein, dodecamers, and trimers͒ of the giant haemoglobin from Eisenia foetida has been characterized by x-ray absorption near edge structure 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 monomers͒ revealing that constraints due to the protein matrix determine the active site geometry and, consequently, the protein function in these large complexes.