دانلود رایگان مقاله لاتین انرژی آنتن برداشت نور از سایت الزویر
عنوان فارسی مقاله:
انرژی آنتن برداشت نور: بینش از جانب CP29
عنوان انگلیسی مقاله:
Energizing the light harvesting antenna: Insight from CP29
سال انتشار : 2016
مقدمه انگلیسی مقاله:
1. Introduction
The photosynthetic apparatus contributes to the fixation of atmospheric CO2 and evolution of O2 [1]. Photosystem II (PSII) is known as the “engine of life” on earth, as it produces O2, reducing power and proton motive force. PSII consists of the reaction center (RC), the proximal (CP43, CP47), and the outer (LHCII, CP24, CP26 and CP29) antenna [2]. LHCII (Lhcb1–3), CP29 (Lhcb4) and CP26 (Lhcb5) share a common helix-5 (H5) domain (Fig. 1A, B), or previously referred to as helix-D [3–5]. The outer antenna of PSII has a dual role as it absorbs photons, transferring excitation energy to RC for utilization, and it rapidly switches into a dissipating (quenching) state, converting excess energy into heat upon increasing light intensity [6,7]. This non photochemical quenching (NPQ) mechanism is central for crop fitness and tolerance [8]. It is activated by the membrane energization achieved by proton and ion chemiosmotic gradients [9,10]. Nevertheless, despite the significant efforts [6,9], the exact quenching site is still obscure, protein engineering is lacking a target, and this holy grail of photosynthesis remains hidden. Several proposals have appeared over the years for the photoprotective qE component of NPQ. Emphasis has been given on the PsbS role and the deepoxidation of violaxanthin (see for example ref. [11]), but Chl-8 (formerly called Chl b3 or Chl614 in [12]) has been also suggested to dissipate energy interacting with the extended π electrons of Zea [5]. Barros and Kühlbrandt [13] suggested that Zea binds to the PsbS monomers, which in turn interact with the antenna proteins. Horton's and Ruban's groups and coworkers have proposed that a conformational change is triggered by a twist of neoxanthin and Lutein that get closer to Chl 1, 2 and 7 and form the dissipation sink [6,14]. There is also significant experimental and theoretical [6,15,16] evidence that the quenching mechanism involves changes in the chl a-lutein energy transfer. Lampoura et al. [17] have used triplet-minussinglet spectroscopy to show that quenching is associated with such changes. Lastly, Liu et al. [12] have suggested that the small lumenexposed helices [helix 2 and helix 5 (called also helix D)] get protonated and re-orient Chl 8 and Chl 14 (b3) to promote energy transfer to Zea which dissipates excitation energy [18]. It was also recently proposed that the chl-614 binding H5 domain of LHCII in higher plants could serve also as a quenching site, via protein conformational changes [10, 12] or being at the boundaries between LHCII and CP43, involved in a potential energy transfer pathway from LHCII to CP43 and towards PSII core complex [19]. Protein conformational changes are thus of fundamental importance to probe such events. Protein conformational changes are vital to biochemistry and provide targets for protein or inhibitor engineering. Specific protein domains undergo significant, well-defined conformational changes upon stimuli [20], the correlation of which is related to function [21]. The controlled interchange between conformations is guided by free energy surfaces (FES) the calculation of which is a major goal relevant to many research fields in chemistry and biophysics. Antenna proteins of PSII regulate the amount of energy trapping according to external stimuli (membrane energization), in such a way, via a photoprotective cycle [10,22]. It is of fundamental importance to elucidate the details or components of the photoprotective mechanism at atomic scale. Simulation can be the only way in the end that could lead to profound
کلمات کلیدی:
