title: Optimal fold symmetry of LH2 rings on a photosynthetic membrane.
abstract: An intriguing observation of photosynthetic light-harvesting systems is the N-fold symmetry of light-harvesting complex 2 (LH2) of purple bacteria. We calculate the optimal rotational configuration of N-fold rings on a hexagonal lattice and establish two related mechanisms for the promotion of maximum excitation energy transfer (EET). (i) For certain fold numbers, there exist optimal basis cells with rotational symmetry, extendable to the entire lattice for the global optimization of the EET network. (ii) The type of basis cell can reduce or remove the frustration of EET rates across the photosynthetic network. We find that the existence of a basis cell and its type are directly related to the number of matching points S between the fold symmetry and the hexagonal lattice. The two complementary mechanisms provide selection criteria for the fold number and identify groups of consecutive numbers. Remarkably, one such group consists of the naturally occurring 8-, 9-, and 10-fold rings. By considering the inter-ring distance and EET rate, we demonstrate that this group can achieve minimal rotational sensitivity in addition to an optimal packing density, achieving robust and efficient EET. This corroborates our findings i and ii and, through their direct relation to S, suggests the design principle of matching the internal symmetry with the lattice order.
authors: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors: Liam
authors: L
authors: Cleary
authors: Hang
authors: H
authors: Chen
authors: Chern
authors: C
authors: Chuang
authors: Robert J
authors: RJ
authors: Silbey
authors: Jianshu
authors: J
authors: Cao
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry* / Q000201:enzymology; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding; D012241:Rhodopseudomonas / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes
references: Structure. 1996 May 15;4(5):581-97
references: 8736556
references: Proc Natl Acad Sci U S A. 2004 Aug 3;101(31):11293-7
references: 15273291
references: Photosynth Res. 2009 Nov-Dec;102(2-3):197-211
references: 19266309
references: Proc Natl Acad Sci U S A. 2012 Jan 17;109(3):706-11
references: 22215585
references: J Phys Chem A. 2009 Dec 17;113(50):13825-38
references: 19929005
references: J Struct Biol. 2005 Dec;152(3):221-8
references: 16330228
references: Nano Lett. 2010 Apr 14;10(4):1450-7
references: 20232894
references: Faraday Discuss. 2012;155:27-41; discussion 103-14
references: 22470965
references: Nature. 2004 Aug 26;430(7003):1058-62
references: 15329728
references: Nano Lett. 2011 Nov 9;11(11):4693-6
references: 22008014
references: J Phys Chem B. 2011 Jul 21;115(28):8821-31
references: 21650216
references: J Mol Biol. 1997 May 2;268(2):412-23
references: 9159480
references: Nano Lett. 2011 Nov 9;11(11):4897-901
references: 21972866
references: Biochim Biophys Acta. 2010 Nov;1797(11):1780-94
references: 20655292
references: J Am Chem Soc. 2008 Jul 16;130(28):8892-3
references: 18570413
references: Proc Natl Acad Sci U S A. 2004 Dec 28;101(52):17994-9
references: 15601770