(589d) Atomic-Level Stresses On Proteins Upon Vitrification

Lyophilization is commonly used in the pharmaceutical and food processing industries to preserve labile biomolecules, but a comprehensive molecular understanding of the process is lacking. This procedure generates both freezing and drying stresses due to the growth of free volume. These stresses, as well as aging in the glass state, can result in undesired molecular mobility which leads to the loss of secondary protein structure [1, 2]. We use molecular dynamics simulations to study the normal and shear stresses acting on individual protein atoms as a result of quenching at constant pressure. We study both isobaric inherent structures and glasses formed via finite-rate quenches. Stresses are calculated on two different proteins, the bee-venom protein melittin and the globular protein ubiquitin, with an atomic-level description of the stress tensor [3]. Protein atoms along the backbone of alpha-helix structures exhibit large increases in the local normal stress after quenching. Many of the atoms which display significant increases belong to carbonyl and amine groups along the protein backbone. These groups are responsible for the formation of hydrogen bonds which stabilize the alpha-helix structure and the increased stress may lead to the degradation of secondary structure.

[1] Webb, S.D., Cleland, J.L., Carpenter, J.F., and Randolph, T.W., J. Pharmaceut. Sci., 92(4), 715, 2003.

[2] Heller, M.C., Caprenter, J.F., and Randolph, T.W., Biotechnol. Bioeng., 63(2), 166, 1999.

[3] Max Born and Kun Huang. Dynamical Theory of Crystal Lattices. Clarendon Press, Oxford, 1954.