Dr. Arvi Freiberg
Department of Biophysics and Plant Physiology
Tartu University
Estonia

Monday, September 28, 2009
3:00 pm (CT)
3269 Beckman Institute

Abstract

Protein function is determined by its properly folded conformation. Denatured conformations can result in disease. Understanding of protein stability with respect to unfolding, e.g., through changing general physical parameters such as temperature and pressure, is thus important. This lecture will review effects of high hydrostatic pressure reaching 2.5 GPa on various integral membrane proteins involved in photosynthesis in plants and bacteria. Native chlorophyll, bacteriochlorophyll, and carotenoid chromophore co-factors of these proteins are used as intrinsic probes to monitor conformational changes of the binding sites. Surprising resilience even to extreme pressures is demonstrated when the proteins are protected by a native lipid bilayer. Yet, significant alterations to the tertiary structure, including breakage of hydrogen bonds to the chromophores are seen when the denatured proteins are extracted from their native membrane environment. In this case, considerable variability of elastic properties of the extracted proteins is observed, tentatively assigned to heterogeneous protein packing in detergent micelles. Genetically modified proteins tend to disintegrate more easily under high pressure compared with the wild type proteins, frequently releasing parts of their chromophore content. Presence of co-solvents (glycerol) and aggregation appears to stabilize the proteins. Most of these pressure effects are reversible, allowing reliable analysis of the thermodynamic equilibrium between native and denatured states. The work presented emphasizes both the high-pressure spectroscopy as an effective tool and pigmented photosynthetic proteins as useful model systems for studies of the stability of integral membrane proteins.