The Magic of Disaccharide Glass Matrices for Protein Function as Decoded by High-Field EPR and FTIR Spectroscopy

Abstract

The structural and dynamical interaction of proteins with their microenvironment in disordered matrices plays a decisive role for their function; EPR spectroscopy is a powerful tool for shading light onto the molecular mechanisms of this protein-matrix interplay. To clarify the molecular mechanisms of disaccharide bioprotection, we studied the structure and dynamics of spin-labeled systems and photosynthetic reaction centers (RCs) in sucrose and trehalose matrices at different hydration levels by means of cw and pulse high-field 95 GHz (W-band) EPR as well as by FTIR. In this minireview, we summarize and discuss EPR and FTIR experiments showing that the anhydrobiotic state of the RC-trehalose system (1) is not the result of matrix-induced changes of the local structure of the charge-separated radical-pair cofactors, P Áþ 865 and Q ÁÀ A , and (2) is not the result of changes of local dynamics and local hydrogen bonding of Q A in its binding pocket. Rather, the extreme impairment of RC dynamics caused by incorporation into the dehydrated trehalose matrix, which also protects it against thermal denaturation, originates in the high rigidity, already at room temperature, of the dry trehalose glass matrix coating the RC protein surface. This surface hydrogen-bonding scaffold shifts the correlation time of thermal conformational fluctuations into the non-biological time domain. Another intriguing aspect of disaccharide bioprotection is the superior The authors dedicate this work to Giovanni Giacometti on the occasion of his 85th birthday. AppliedMagnetic Resonance efficiency of trehalose versus sucrose matrices in stabilizing the anhydrobiotic state of proteins. To clarify the molecular basis of this specificity, glassy trehalose-water and sucrose-water binary systems, incorporating a nitroxide radical as spin probe, have been studied by high-field W-band EPR spectroscopy at different water contents. Analysis of the EPR spectra revealed a different structural and dynamical organization in the sucrose and trehalose matrix, only the trehalose being homogeneous in terms of residual water and nitroxide distribution.

Red Shift in the Absorption Spectrum of Phototropin LOV1 upon the Formation of a Semiquinone Radical: Reconstructing the Orbital Architecture

“…Interestingly, the chromophore is not as much influenced by the stabilization process as the tryptophan residue. This has similarly been observed in photosynthetic reaction centers embedded in a trehalose matrix . Here, the motional dynamics of quinone Q A in its anionic radical state after electron transfer from the special pair remained the same and was not influenced by the changes in the local environment.…”

“…This has similarly been observed in photosynthetic reaction centers embedded in a trehalose matrix. 66 Here, the motional dynamics of quinone Q A in its anionic radical state after electron transfer from the special pair remained the same and was not influenced by the changes in the local environment. The authors concluded that the observed change in radical-pair recombination rate originates from increased rigidity of the surrounding protein due to its surface interaction with the dry trehalose glass.…”

Synthesis and Electron Spin Relaxation of Tetracarboxylate Pyrroline Nitroxides

“…37 Trehalose also maintains protein function and enzyme activity better than dehydrated sucrose. 38,39 Glasses containing 10% sucrose were observed to be more stable during drying than 100% trehalose glasses. If the glass crystallizes, the solute is excluded from the lattice which results in locally high concentrations of solute that enhance relaxation rates (Figure S4, SI).…”

Special Issue of Applied Magnetic Resonance Celebrating the 85th Birthdays of Klaus Möbius and Kev M. Salikhov

“…This sugar plays an important role in anhydrobiosis ("life without water"), e.g., in desert environments (in "resurrection plants" and some microorganisms). The combined approach of fast optical and FTIR spectroscopy and high-field EPR techniques led to a model for the protecting effect of the sugar matrix on the investigated protein with implications for photosynthesis in arid and hot environments [16].…”