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Volume 11
Journal of Proteomics & Bioinformatics
ISSN: 0974-276X
Structural Biology 2018
September 24-26, 2018
September 24-26, 2018 | Berlin, Germany
14
th
International Conference on
Structural Biology
Computational study of LH2 complexes from purple bacteria and its structural adaptation to the
dark environments
Felipe Cardoso Ramos, Stefano Caprasecca, Lorenzo Cupellini
and
Benedetta Mennucci
Università di Pisa, Italy
Statement of the Problem:
The light harvesting apparatus of typical purple photosynthetic bacteria is composed by the LH1
and LH2 complexes, which act together in the absorption and transfer of light energy to the photosynthetic reaction center
(RC). The LH2 complexes are circular membrane proteins formed by nine dimeric apoproteins, the α and β chains, bound to
one carotenoid (Car) molecule and three bacteriochlorophyll a (Bchl) molecules (B800, B850α and B850β). Purple bacteria
express LH2 complexes with different αβ apo-proteins depending on the light intensity, which allows them to adapt to the
luminosity conditions. The species
Rhodopseudomonas acidophila
(Rps. acidophila), for example, produces LH2 complexes
with absorption at 800 and 850 nm (B800-850) when in high light (HL) conditions, but when in low light (LL) conditions they
are replaced by complexes that absorb at 800 and 820 nm (B800-820).
Methodology & Theoretical Orientation:
Here, we performed classical molecular dynamics (MD) simulations of LH2
complexes from purple bacteria in lipid membranes, aimed to generate atomistic models for these light harvesting complexes,
focusing on the genus
Rhodopseudomonas
.
Findings:
Analysing the trajectories obtained, we verified that the size and the circular shape of complexes were well preserved
along the simulations. In addition, our simulations were able to reproduce the main protein pigments interactions described
in the crystallographic structures.
Conclusion & Significance:
Through the simulation protocol applied it was possible to produce equilibrated models for
entire HL and LL LH2 complexes in membranes. These models are currently been employing in hybrid quantum mechanics/
molecular mechanics (QM/MM) calculations which will allow us to simulate the absorption spectra of the complexes. At the
end of this study, we hope to provide detailed structural explanations about the occurrence of different spectra and contribute
to the understanding of the molecular mechanisms that govern the purple bacteria adaptation to dark environments.