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111.
W. C. W. Nixon 《BMJ (Clinical research ed.)》1937,2(4002):579-581
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Peter J. Nixon Franck Michoux Jianfeng Yu Marko Boehm Josef Komenda 《Annals of botany》2010,106(1):1-16
Background
Photosystem II (PSII) is the light-driven water:plastoquinone oxidoreductase of oxygenic photosynthesis and is found in the thylakoid membrane of chloroplasts and cyanobacteria. Considerable attention is focused on how PSII is assembled in vivo and how it is repaired following irreversible damage by visible light (so-called photoinhibition). Understanding these processes might lead to the development of plants with improved growth characteristics especially under conditions of abiotic stress.Scope
Here we summarize recent results on the assembly and repair of PSII in cyanobacteria, which are excellent model organisms to study higher plant photosynthesis.Conclusions
Assembly of PSII is highly co-ordinated and proceeds through a number of distinct assembly intermediates. Associated with these assembly complexes are proteins that are not found in the final functional PSII complex. Structural information and possible functions are beginning to emerge for several of these ‘assembly’ factors, notably Ycf48/Hcf136, Psb27 and Psb28. A number of other auxiliary proteins have been identified that appear to have evolved since the divergence of chloroplasts and cyanobacteria. The repair of PSII involves partial disassembly of the damaged complex, the selective replacement of the damaged sub-unit (predominantly the D1 sub-unit) by a newly synthesized copy, and reassembly. It is likely that chlorophyll released during the repair process is temporarily stored by small CAB-like proteins (SCPs). A model is proposed in which damaged D1 is removed in Synechocystis sp. PCC 6803 by a hetero-oligomeric complex composed of two different types of FtsH sub-unit (FtsH2 and FtsH3), with degradation proceeding from the N-terminus of D1 in a highly processive reaction. It is postulated that a similar mechanism of D1 degradation also operates in chloroplasts. Deg proteases are not required for D1 degradation in Synechocystis 6803 but members of this protease family might play a supplementary role in D1 degradation in chloroplasts under extreme conditions. 相似文献117.
Chloroplast transformation offers an exciting platform for the safe, inexpensive and large-scale production of recombinant
proteins in plants. An important advantage for the isolation of proteins produced in the chloroplast would be the use of affinity
tags for rapid purification by affinity chromatography. To date, only His-tags have been used. In this study, we have tested
the feasibility of expressing two additional affinity tags: glutathione-S-transferase (GST) and a His-tagged derivative of the maltose-binding protein (His6-MBP). By using the chloroplast 16S rRNA promoter and 5′ untranslated region of phage T7 gene 10, GST and His6-MBP were expressed in homoplastomic tobacco plants at approximately 7% and 37% of total soluble protein, respectively. GST
could be purified by one-step-affinity purification using a glutathione column. Much better recoveries were obtained for His6-MBP by using a twin-affinity purification procedure involving first immobilised nickel followed by binding to amylose. Interestingly,
expression of GST led to cytoplasmic male sterility. Overall, our work expands the tools available for purifying recombinant
proteins from the chloroplast. 相似文献
118.
Plants, algae and cyanobacteria grow because of their ability to use sunlight to extract electrons from water. This vital reaction is catalysed by the Photosystem II (PSII) complex, a large multi-subunit pigment-protein complex embedded in the thylakoid membrane. Recent results show that assembly of PSII occurs in a step-wise fashion in defined regions of the membrane system, involves conserved auxiliary factors and is closely coupled to chlorophyll biosynthesis. PSII is also repaired following damage by light. FtsH proteases play an important role in selectively removing damaged proteins from the complex, both in chloroplasts and cyanobacteria, whilst undamaged subunits and pigments are recycled. The chloroplastic Deg proteases play a supplementary role in PSII repair. 相似文献
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Chloroplast transformation provides an inexpensive, easily scalable production platform for expression of recombinant proteins in plants. However, this technology has been largely limited to the production of soluble proteins. Here we have tested the ability of tobacco chloroplasts to express a membrane protein, namely plastid terminal oxidase 1 from the green alga Chlamydomonas reinhardtii (Cr-PTOX1), which is predicted to function as a plastoquinol oxidase. A homoplastomic plant containing a codon-optimised version of the nuclear gene encoding PTOX1, driven by the 16S rRNA promoter and 5'UTR of gene 10 from phage T7, was generated using a particle delivery system. Accumulation of Cr-PTOX1 was shown by immunoblotting and expression in an enzymatically active form was confirmed by using chlorophyll fluorescence to measure changes in the redox state of the plastoquinone pool in leaves. Growth of Cr-PTOX1 expressing plants was, however, more sensitive to high light than WT. Overall our results confirm the feasibility of using plastid transformation as a means of expressing foreign membrane proteins in the chloroplast. 相似文献
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