X-ray Crystallography of Hemoglobins

X-ray crystallography has played a key role in understanding the relationship between protein structure and physiological function. In particular, X-ray analysis of hemoglobin (Hb) crystals has been pivotal in the formulation of basic theories concerning the behavior of allosteric proteins. Methemoglobin (MetHb) from horse was the first three-dimensional (3D) structure of liganded Hb to be solved (1 –4 ). It was followed by crystallographic determination of the unliganded (deoxygenated) form nearly a decade later (5 ). The X-ray analyses provided 3D atomic resolution structures and confirmed that Hb was tetrameric, containing two subunit types (α and β), and one oxygen-binding heme group per subunit. John Kendrew (myoglobin) and Max Perutz (Hb) received the Nobel Prize for their pioneering work, being the first to determine the 3D structures of proteins, using X-ray crystallography. Since the crystallographic determination of these structures, there has been an almost exponential increase in the use of X-ray crystallography to determine the 3D structures of proteins, i.e., as evidenced by the history of structures deposited in the protein data bank.