Biomolecules may have different and complicated structures and dynamics, leading to different functions. These aspects are linked, namely a biomolecule performs its functions if its native structure and dynamics do not change upon external perturbations, and viceversa . If a protein is stored as a lyophilized system without any excipient, its native structure turns to be destroyed or modified irreversibly by the freeze-drying process [2, 3]. To improve their long-term storage and stability, biomolecules are stored as lyophilized mixtures in presence of glassy H-bonded matrices . For this reason, saccharides and polyols are usually added to the formulation to preserve the native structure of biomolecules, protecting them by the stresses due to the eradication of water , increasing the mixtures stability because of their higher viscosities compared to water.
Mid-Infrared measurements give us indirect information on the state of the native secondary structure , important to quantify the real bioprotection exerted by the glassy solvents used. In the present work we have studied lysozyme embedded in different bioprotectant matrices, such as sugars and polyols. A complementary technique can be UV stimulated Raman (in normal and resonant mode) able to provide information on the amide bands and to the behaviour of particular residues and groups .
The systems under study were obtained from freeze-drying procedure. Mid-Infrared and UV-Raman spectra are very sensitive to the modification of the secondary structure of the biomolecules, allowing us to quantify these changes, with varying temperature and glassy solvent. In particular, after lyophilization and at ambient temperature, it has been observed a decreasing of the alpha-helix population depending on the solvent used as bioprotectors and a simultaneous augmentation of the other secondary structures. Moreover, increasing temperature towards denaturation, the modification of the secondary structure becomes stronger with a further destabilization of the native alpha-helix population in favour of beta-sheets and random structures.
Aknowledgements: we thank the CERIC-ERIC program for the time shifts granted for the experiment at IUVS and SISSI beamline - Elettra Synchrotron Trieste.
1. Fenimore P. W., Frauenfelder H., McMahon B. H., Parak F. G., Proc. Natl. Acad. Sci. USA. 99, 14408–14413 (2002).
2. Carpenter J.F., Crowe J.H, Biochem. J. 28, 3916-3922 (1989).
3. Petrelski S. J., Pikal K. A., Arakawa T., Pharm. Res. 12, 1250-1259 (1995).
4. Allison S.D., Chang B., Randolph T.W., Carpenter J.F., Arch. Biochem. Biophys. 365, 289-298 (1999).
5. Dong A., Huang P., Caughey W. S.,, Biochem. 29, 3303-3308 (1990).
6. Oladepo S. A. , Xiong K.,Hong Z., Asher S.A:, Handen J, Lednev I.K., Chem. Rev. 112, 2604–2628 (2012)