Professor C. Neil Hunter
Molecular Biology and Biotechnology
The University of Sheffield
South Yorkshire, UK

Thursday, June 23, 2011
3:00 pm (CT)
3269 Beckman Institute

Abstract

Light harvesting and energy trapping in photosynthesis is achieved by macromolecular membrane assemblies, which bind thousands of chlorophylls, held in specific orientations and in close proximity to one another in order to ensure efficient energy transfer. The structures of light-harvesting (LH) and reaction center (RC) complexes, determined by crystallographic methods over the last 25 years, have been profoundly important in furthering our understanding of these early stages in photosynthesis. Thus, we know a great deal about the internal arrangements of chlorophyll-protein complexes that foster efficient harvesting of solar energy, its transmission to RCs, and trapping of this excitation energy as a stable charge separation. Given that many LH and RC complexes are found grouped together in photosynthetic membranes, it is necessary to understand the next level of structural information, namely the supramolecular organization of individual complexes to form a 'photosynthetic unit'. The size and irregular structures of such assemblies preclude analysis by crystallographic and other averaging methods. However, in the simplest case of bacterial photosynthesis, atomic force microscopy has made inroads into this difficult structural problem, revealing the architecture of photosynthetic membranes in sufficient detail to allow docking of atomic structures into membrane maps. Combinations of atomic force microscopy, linear dichroism, cryo-electron microscopy and computational methods have allowed construction of models of whole membrane assemblies, which take into account spectroscopic data on energy transfer and trapping. Such models are starting to address the collective behavior of whole membrane assemblies, to make predictions of the energy transfer and trapping behavior of large- scale arrays, and to identify desirable design motifs for artificial photosynthetic systems. New surface chemistries and patterning methods are being developed to facilitate the creation of innovative architectures for coupled energy transfer and trapping. Nanometer and micron-scale patterns of photosynthetic complexes have been fabricated on self-assembled monolayers deposited on either gold or glass, using near-field photolithographic methods. Such artificial LH arrays will advance our understanding of natural energy-converting systems, and could guide the design and production of proof-of-principle devices for biomimetic systems to capture, convert and store solar energy.