Light-induced protein-matrix uncoupling and protein relaxation in dry samples of trehalose-coated MbCO at room temperature |
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Authors: | Stefania Abbruzzetti Sergio Giuffrida Silvia Sottini Cristiano Viappiani Lorenzo Cordone |
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Institution: | (1) Istituto Nazionale di Fisica della Materia, Universitá di Parma, Parco area delle Scienze n. 7A, 43100 Parma, Italy;(2) Dipartimento di Fisica, Universitá di Parma, Parco area delle Scienze n. 7A, 43100 Parma, Italy;(3) Dip. di Scienze Fisiche ed Astronomiche, Universitá di Palermo, Via Archirafi 36, 90123 Palermo, Italy |
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Abstract: | In humid samples of trehalose-coated carboxy-myoglobin (MbCO), thermally driven conformational relaxation takes place after
photodissociation of the carbon monoxide (CO) molecule at room temperature. In such samples, because of the extreme viscosity
of the external matrix, photodissociated CO cannot diffuse out of the protein and explores the whole (proximal and distal
side) heme pocket, experiencing averaged protein heme pocket structures, as a results of the presence of Brownian motions.
At variance, in very dry samples, a lower portion of the photodissociated CO diffuses from the distal to the proximal heme
pocket side probing in nonaveraged structures. We revisit here the flash photolysis data by Librizzi et al. (2002) and report
on new, room temperature experiments in MbCO-trehalose samples, shortly illuminated prior the laser pulse. In dry samples,
pre-illumination increased the diffusion of CO from the distal to the proximal heme pocket side, which resulted in less structure
than in non-pre-illuminated samples. Such an effect, which is absent in humid samples, stems from a decoupling of the protein
internal degrees of freedom from those of the external water-sugar matrix. We suggest that such a decoupling can be brought
about by the continuous attempts performed by the protein during pre-illumination to undergo relaxation toward the photodissociated
deoxy state. This, in turn, causes a collapse in the hydrogen bond network, which connects the protein surface to the water-sugar
matrix, as reported by Cottone et al. (2002) and Giuffrida et al. (2003). In the conclusion section, we discuss the possible
involvement of the processes invoked to rationalize the present data, in the function of macromolecules and interactions in
living cells. |
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Keywords: | Trehalose flash-photolysis light-induced relaxation myoglobin hydrogen bonds |
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