Award details

The structure and function of purple bacterial antenna complexes

Reference	BB/D000610/1
Principal Investigator / Supervisor	Professor Richard Cogdell
Co-Investigators / Co-Supervisors	Professor Neil William Isaacs
Institution	University of Glasgow
Department	School of Life Sciences
Funding type	Research
Value (£)	287,513
Status	Completed
Type	Research Grant
Start date	01/11/2005
End date	31/10/2008
Duration	36 months

Abstract

The antenna system of most purple bacteria is composed of two types of antenna complexes, the RC/LH1 core complex and the LH2 complexes. These complexes are integral membrane proteins and are constructed on the same modular principle. They are circular (LH2) or elliptical (RC/LH1) oligomers of low molecular weight heterodimers consisting of ab apoproteins and, in the case of LH1, the RC is hole in the middle. Over many years we have been studying the structure and function of these pigment-protein complexes. Previously we determined the structure of these LH2 complexes from Rps. acidophila to a resolution of 2.0Ang and more recently described the first structure of an RC/LH1 core complex to an intermediate resolution of 4.8Ang Fig.1. The major aim of the present proposal is to improve the crystals of the RC/LH1 core complex in order to get a high-resolution structure. The LH1 complex must allow the exchange of ubiquinone between the enclosed RC and the rest of the cyclic electron transport pathway. Our 4.8Ang structure indicates that an as yet uncharacterised protein, W, is central to this. We shall fully characterise W and hopefully a high-resolution structure will reveal how it functions as a gate. In parallel we will continue our successful programme of advanced biophysical studies to investigate the mechanisms of the various energy transfer reactions which take place within and between the antenna complexes. Recently, using 10-15fs excitation pulses, we have discovered what appears to be a new carotenoid excited singlet state. We now need to investigate its involvement in carotenoid energy transfer to the Bchls. Many energy transfer reactions require the differentiation between dynamic and static disorder if the detailed mechanisms involved are to be correctly described. These questions can only be addressed using single molecule experiments, and we shall use this approach to help unravel the detailed mechanisms of the energy transfer reactions. Very recently beautiful AFM pictures have shown that the organisation of the antenna complexes in vivo is very variable, depending both on the species and the growth conditions. So far there are no data indicating how different membrane architectures affect overall light-harvesting performance. We intend to apply a combination of advanced imaging techniques and energy transfer studies to investigate this fundamental question.

Summary

All life on earth depends on photosynthesis. Ultimately it provides all the food we eat, all the oxygen we breathe and represents the only net input of energy into the biosphere. Photosynthesis begins when light is absorbed by the light-harvesting pigments (chlorophylls and carotenoids). The absorbed light energy is then quickly and efficiently transferred to a specialised pigment-protein complex, called the reaction centre, where the light energy is trapped and converted into chemical energy. Now photosynthesis has really begun. The research in this proposal aims to describe the structure of the light harvesting system and to understand how it works. Purple bacteria are used, rather than plants, because their pigment-protein complexes are more robust and easier to work with. Moreover previous studies have clearly shown that the basic concepts discovered in the purple bacterial system are applicable to all photosynthetic organisms.

Committee	Closed Committee - Biomolecular Sciences (BMS)
Research Topics	Microbiology, Structural Biology
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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