Structure-based simulation of linear optical spectra of the CP43 core antenna of photosystem II

The linear optical spectra (absorbance, linear dichroism, circular dichroism, fluorescence) of the CP43 (PsbC) antenna of the photosystem II core complex (PSIIcc) pertaining to the S(0) → S(1) (Q(Y)) transitions of the chlorophyll (Chl) a pigments are simulated by applying a combined quantum chemical/electrostatic method to obtain excitonic couplings and local transition energies (site energies) on the basis of the 2.9 Å resolution crystal structure (Guskov et al., Nat Struct Mol Biol 16:334-342, 2009). The electrostatic calculations identify three Chls with low site energies (Chls 35, 37, and 45 in the nomenclature of Loll et al. (Nature 438:1040-1044, 2005). A refined simulation of experimental spectra of isolated CP43 suggests a modified set of site energies within 143 cm(-1) of the directly calculated values (root mean square deviation: 80 cm(-1)). In the refined set, energy sinks are at Chls 37, 43, and 45 in agreement with earlier fitting results (Raszewski and Renger, J Am Chem Soc 130:4431-4446, 2008). The present structure-based simulations reveal that a large part of the redshift of Chl 37 is due to a digalactosyldiacylglycerol lipid. This finding suggests a new role for lipids in PSIIcc, namely the tuning of optical spectra and the creation of an excitation energy funnel towards the reaction center. The analysis of electrostatic pigment-protein interactions is used to identify amino acid residues that are of potential interest for an experimental approach to an assignment of site energies and energy sinks by site-directed mutagenesis

Lessons from Natural Cold-Induced Dormancy to Organ Preservation in Medicine and Biotechnology: From the “Backwoods to the Bedside”

Hypothermia is a powerful modulator of all life processes, and this has been harnessed over the past 50 years in clinical sciences where tissues or organs for transplantation need to be stored outside the body for periods of time. However for human organs (as an obligate homoeothermic), cooling alone cannot provide sufficient time for the clinical logistics of transplantation, and a series of interventions to further control metabolism have been developed empirically. In retrospect, it can be seen that these approaches mimic to some degree the ways in which cold tolerance in the natural world has developed in evolutionary terms. This chapter reviews the history and the current state of the art of applied hypothermic preservation, and compares and contrasts what is known about natural cold tolerance, highlighting areas for further research and development to meet the challenges for organ and tissue preservation in the next few years. © 2010 Springer-Verlag Berlin Heidelberg