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Spontaneous Quaternary and Tertiary T-R Transitions of Human Hemoglobin in Molecular Dynamics Simulation

Figure 7

Populations of tertiary states of the α (black) and β (grey) subunits as a function of quaternary state (T/R) and the HC3 protonation.

The tertiary states were computed from the projections of the subunit structures during simulation onto the tertiary difference vectors connecting the T and R tertiary X-ray structures, denoted by t and r. The projections were normalized such that the r and t tertiary structure correspond to a projection of −1 and +1, respectively. A simulation frame was assigned to the R or to the T quaternary structure, if the projection onto the vector connecting the R and T quaternary states was <−0.5 or >+0.5, respectively (compare Fig. 5). Populations in Hb simulations without deprotonated His(β)146 are denoted by ‘T/R no HC3’ (A/B), and simulations with protonated His(β)146 are denoted by ‘T/R HC3’ (C/D).

Figure 7