title: N-terminal processing of Lhca3 Is a key step in remodeling of the photosystem I-light-harvesting complex under iron deficiency in Chlamydomonas reinhardtii.
abstract: Iron deficiency induces a remodeling of the photosynthetic apparatus in Chlamydomonas reinhardtii. In this study we showed that a key mechanistic event in the remodeling process of photosystem I (PSI) and its associated light-harvesting proteins (LHCI) is the N-terminal processing of Lhca3. N-terminal processing of Lhca3 is documented independently by two-dimensional gel electrophoresis and tandem mass spectrometric (MS/MS) analysis as well as by quantitative comparative MS/MS peptide profiling using isotopic labeling of proteins. Dynamic remodeling of the LHCI complex under iron deficiency is further exemplified by depletion of Lhca5 and up-regulation of Lhca4 and Lhca9 polypeptides in respect to photosystem I. Most importantly, the induction of N-terminal processing of Lhca3 by progression of iron deficiency correlates with the functional drop in excitation energy transfer efficiency between LHCI and PSI as assessed by low temperature fluorescence emission spectroscopy. Using an RNA interference (RNAi) strategy, we showed that the truncated form of Lhca3 is essential for the structural stability of LHCI. Depletion of Lhca3 by RNAi strongly impacted the efficiency of excitation energy transfer between PSI and LHCI, as is the case for iron deficiency. However, in contrast to iron deficiency, comparative MS/MS peptide profiling using isotopic labeling of proteins demonstrated that RNAi depletion of Lhca3 caused strong reduction of almost all Lhca proteins in isolated PSI particles.
authors.affiliation: Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Bianca
authors.initials: B
authors.lastname: Naumann
authors.forename: Einar J
authors.initials: EJ
authors.lastname: Stauber
authors.forename: Andreas
authors.initials: A
authors.lastname: Busch
authors.forename: Frederik
authors.initials: F
authors.lastname: Sommer
authors.forename: Michael
authors.initials: M
authors.lastname: Hippler
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004735:Energy Transfer; D007501:Iron / Q000502:physiology*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D034622:RNA Interference; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D010446:Peptide Fragments; D045331:Photosystem I Protein Complex; D007501:Iron; D014357:Trypsin