title: Understanding the electronic energy transfer pathways in the trimeric and hexameric aggregation state of cyanobacteria phycocyanin within the framework of Förster theory.
abstract: In the present study, the electronic energy transfer pathways in trimeric and hexameric aggregation state of cyanobacteria C-phycocyanin (C-PC) were investigated in term of the Förster theory. The corresponding excited states and transition dipole moments of phycocyanobilins (PCBs) located into C-PC were examined by model chemistry in gas phase at time-dependent density functional theory (TDDFT), configuration interaction-singles (CIS), and Zerner's intermediate neglect of differential overlap (ZINDO) levels, respectively. Then, the long-range pigment-protein interactions were approximately taken into account by using polarizable continuum model (PCM) at TDDFT level to estimate the influence of protein environment on the preceding calculated physical quantities. The influence of the short-range interaction caused by aspartate residue nearby PCBs was examined as well. Only when the protonation of PCBs and its long- and short-range interactions were properly taken into account, the calculated energy transfer rates (1/K) in the framework of Förster model at TDDFT/B3LYP/6-31+G* level were in good agreement with the experimental results of C-PC monomer and trimer. Furthermore, the present calculated results suggested that the energy transfer pathway in C-PC monomer is predominant from β-155 to β-84 (1/K = 13.4 ps), however, from α-84 of one monomer to β-84 (1/K = 0.3-0.4 ps) in a neighbor monomer in C-PC trimer. In C-PC hexamer, an additional energy flow was predicted to be from β-155 (or α-84) in top trimer to adjacent β-155 (or α-84) (1/K = 0.5-2.7 ps) in bottom trimer.
authors.affiliation: Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, Department of Chemistry, Central China Normal University, Wuhan 430079, People's Republic of China.
authors.forename: Yanliang
authors.initials: Y
authors.lastname: Ren
authors.forename: Bo
authors.initials: B
authors.lastname: Chi
authors.forename: Osama
authors.initials: O
authors.lastname: Melhem
authors.forename: Ke
authors.initials: K
authors.lastname: Wei
authors.forename: Lingling
authors.initials: L
authors.lastname: Feng
authors.forename: Yongjian
authors.initials: Y
authors.lastname: Li
authors.forename: Xinya
authors.initials: X
authors.lastname: Han
authors.forename: Ding
authors.initials: D
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jian
authors.initials: J
authors.lastname: Wan
authors.forename: Xin
authors.initials: X
authors.lastname: Xu
authors.forename: Minghui
authors.initials: M
authors.lastname: Yang
mesh_terms: D003198:Computer Simulation; D000458:Cyanobacteria / Q000737:chemistry*; D031541:Fluorescence Resonance Energy Transfer; D015394:Molecular Structure; D010798:Phycocyanin / Q000737:chemistry*
chemical_list: D010798:Phycocyanin