Abstract
The quaternary transition between the relaxed (R) and tense (T) states of heme-binding proteins is a textbook example for the allosteric structural transition. Homodimeric hemoglobin (HbI) from Scapharca inaequivalvis is a useful model system for investigating the allosteric behavior because of the relatively simple quaternary structure. To understand the cooperative transition of HbI, wild-type and mutants of HbI have been studied by using time-resolved X-ray solution scattering (TRXSS), which is sensitive to the conformational changes. Herein, we review the structural dynamics of HbI investigated by TRXSS and compare the results of TRXSS with those of other techniques.
Highlights
As a prime example of the allostery, the quaternary structural transition of human tetrameric hemoglobin (Hb) induced by ligand binding and dissociation has been investigated extensively [1,2,3,4,5,6,7]
time-resolved X-ray solution scattering (TRXSS) data of F97Y HbI were analyzed by using the same method applied for WT HbI [21]
Similar to F97Y HbI, the TRXSS data of T72V HbI can be explained by the same kinetic model of WT HbI (Figure 4c) [24]
Summary
As a prime example of the allostery, the quaternary structural transition of human tetrameric hemoglobin (Hb) induced by ligand binding and dissociation has been investigated extensively [1,2,3,4,5,6,7]. In the HbI, the E and F helices of monomers are located at the interface of homodimer [11,12,39], which is often referred to as EF dimer This EF dimer structure has been found in tetrameric hemoglobin from Caudina arenicola [40] and erythrocruorin from Lumbricus terrestris, which is a megadalton complex including 144 hemoglobin subunits and 36 linker subunits [41]. In this respect, studies on the allostery of HbI would provide a clue for understanding the structural dynamics of the larger and complex hemoglobin.
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