Trehalose is a non-reducing disaccharide of glucose found in organisms, which can survive adverse conditions such as extreme drought and high temperatures. Furthermore, isolated structures, as enzymes or liposomes, embedded in trehalose are preserved against stressing conditions [see e.g. Crowe LM (2002) Comp Biochem Physiol A 131:505-513]. Among other hypotheses, such protective effect has been suggested to stem, in the case of proteins, from the formation of a water-mediated, hydrogen bond network, which anchors the protein surface to the water-sugar matrix, thus coupling the internal degrees of freedom of the biomolecule to those of the surroundings [Giuffrida S, et al. (2003) J Phys Chem B 107:13211-13217]. Analogous protective effect is also accomplished by other saccharides, although with a lower efficiency. Here, we studied the recombination kinetics of the primary, light-induced charge separated state (P+QA-), and the thermal stability of the photosynthetic reaction centre (RC) of Rhodobacter sphaeroides, in trehalose-water and in sucrose-water matrixes of decreasing water content. Our data show that, in sucrose, at variance from trehalose, the system undergoes a “nano phase-separation” when the water/sugar mole fraction is lower than the threshold level ~ 0.8. We rationalise this result assuming that the hydrogen bond network, which anchors the RC surface to its surroundings is formed in trehalose but not in sucrose. We suggest that both the coupling, in the case of trehalose, and the “nano phase-separation”, in the case of sucrose, start at low water content when the components of the system enter in competition for the residual water.
Protein-Matrix Coupling/Uncoupling in “Dry” Systems of Photosynthetic Reaction Centre Embedded in Trehalose/Sucrose: The Origin of Trehalose Peculiarity
PALAZZO, Gerardo;
2008-01-01
Abstract
Trehalose is a non-reducing disaccharide of glucose found in organisms, which can survive adverse conditions such as extreme drought and high temperatures. Furthermore, isolated structures, as enzymes or liposomes, embedded in trehalose are preserved against stressing conditions [see e.g. Crowe LM (2002) Comp Biochem Physiol A 131:505-513]. Among other hypotheses, such protective effect has been suggested to stem, in the case of proteins, from the formation of a water-mediated, hydrogen bond network, which anchors the protein surface to the water-sugar matrix, thus coupling the internal degrees of freedom of the biomolecule to those of the surroundings [Giuffrida S, et al. (2003) J Phys Chem B 107:13211-13217]. Analogous protective effect is also accomplished by other saccharides, although with a lower efficiency. Here, we studied the recombination kinetics of the primary, light-induced charge separated state (P+QA-), and the thermal stability of the photosynthetic reaction centre (RC) of Rhodobacter sphaeroides, in trehalose-water and in sucrose-water matrixes of decreasing water content. Our data show that, in sucrose, at variance from trehalose, the system undergoes a “nano phase-separation” when the water/sugar mole fraction is lower than the threshold level ~ 0.8. We rationalise this result assuming that the hydrogen bond network, which anchors the RC surface to its surroundings is formed in trehalose but not in sucrose. We suggest that both the coupling, in the case of trehalose, and the “nano phase-separation”, in the case of sucrose, start at low water content when the components of the system enter in competition for the residual water.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
