A DO molecule hydrogen-bonded to a Cyt1•Gua20 base pair in the minor groove

<p><b>Copyright information:</b></p><p>Taken from "Complicated water orientations in the minor groove of the B-DNA decamer d(CCATTAATGG) observed by neutron diffraction measurements"</p><p>Nucleic Acids Research 2005;33(9):3017-3024.</p><p>Published online 24 May 2005</p><p>PMCID:PMC1140084.</p><p>© The Author 2005. Published by Oxford University Press. All rights reserved</p> The purple and blue contours indicate

Ligation-Dependent Picosecond Dynamics in Human Hemoglobin As Revealed by Quasielastic Neutron Scattering

Hemoglobin, the vital O₂ carrier in red blood cells, has long served as a classic example of an allosteric protein. Although high-resolution X-ray structural models are currently available for both the deoxy tense (T) and fully liganded relaxed (R) states of hemoglobin, much less is known about their dynamics, especially on the picosecond to subnanosecond time scales. Here, we investigate the picosecond dynamics of the deoxy and CO forms of human hemoglobin using quasielastic neutron scattering under near physiological conditions in order to extract the dynamics changes upon ligation. From the analysis of the global motions, we found that whereas the apparent diffusion coefficients of the deoxy form can be described by assuming translational and rotational diffusion of a rigid body, those of the CO form need to involve an additional contribution of internal large-scale motions. We also found that the local dynamics in the deoxy and CO forms are very similar in amplitude but are slightly lower in frequency in the former than in the latter. Our results reveal the presence of rapid large-scale motions in hemoglobin and further demonstrate that this internal mobility is governed allosterically by the ligation state of the heme group