Pigment and protein composition of reconstituted light-harvesting complexes and effects of some protein modifications |
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| Authors: | Kirk V. Cammarata F. Gerald Plumley Gregory W. Schmidt |
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| Affiliation: | (1) Botany Department, University of Georgia, 30602 Athens, Georgia, USA;(2) Present address: Institute of Marine Science, University of Alaska, 99775-1080 Fairbanks, Alaska, USA |
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| Abstract: | The structure and heterogeneity of LHC II were studied by in vitro reconstitution of apoproteins with pigments (Plumley and Schmidt 1987, Proc Natl Acad Sci 84: 146–150). Reconstituted CP 2 complexes purified by LDS-PAGE were subsequently characterized and shown to have spectroscopic properties and pigment-protein compositions and stoichiometries similar to those of authentic complexes. Heterologous reconstitutions utilizing pigments and light-harvesting proteins from spinach, pea and Chlamydomonas reinhardtii reveal no evidence of specialized binding sites for the unique C. reinhardtii xanthophyll loroxanthin: lutein and loroxanthin are interchangeable for in vitro reconstitution. Proteins modified by the presence of a transit peptide, phosphorylation, or proteolytic removal of the NH2-terminus could be reconstituted. Evidence suggests that post-translational modification are not responsible for the presence of six electrophoretic variants of C. reinhardtii CP 2. Reconstitution is blocked by iodoacetamide pre-treatment of the apoproteins suggesting a role for cysteine in pigment ligation and/or proper folding of the pigment-protein complex. Finally, no effect of divalent cations on pigment reassembly could be detected.Abbreviations cab chlorophyll a/b-binding protein genes - Chl chlorophyll - CP2 light-harvesting chlorophyll A+b-protein complex fractionated by mildly denaturing LDS-PAGE from Photosystem II in thylakoids - CP 43 and CP 47 chlorophyll a-antenna complexes fractionated from Photosystem II in thylakoids by mildly denaturing LDS-PAGE at 4°C - IgG gamma immunoglobulin - LDS lithium dodecyl sulfate - LDS-PAGE lithium dodecyl sulfate polyacrylamide gel electrophoresis at 4°C - LHC I and LHC II thylakoid light-harvesting chlorophyll a+b-protein holocomplexes associated with Photosystems I and II, respectively - PS II Photosystem II - TX100 Triton X-100 - TX100-derived LHC light-harvesting complexes enriched in LHC II following fractionation of thylakoids by TX100 |
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| Keywords: | CP2 LHCP II pigment-protein reconstitution transit peptide xanthophyll |
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