title: Functional analysis of light-harvesting-like protein 3 (LIL3) and its light-harvesting chlorophyll-binding motif in Arabidopsis.
abstract: The light-harvesting complex (LHC) constitutes the major light-harvesting antenna of photosynthetic eukaryotes. LHC contains a characteristic sequence motif, termed LHC motif, consisting of 25-30 mostly hydrophobic amino acids. This motif is shared by a number of transmembrane proteins from oxygenic photoautotrophs that are termed light-harvesting-like (LIL) proteins. To gain insights into the functions of LIL proteins and their LHC motifs, we functionally characterized a plant LIL protein, LIL3. This protein has been shown previously to stabilize geranylgeranyl reductase (GGR), a key enzyme in phytol biosynthesis. It is hypothesized that LIL3 functions to anchor GGR to membranes. First, we conjugated the transmembrane domain of LIL3 or that of ascorbate peroxidase to GGR and expressed these chimeric proteins in an Arabidopsis mutant lacking LIL3 protein. As a result, the transgenic plants restored phytol-synthesizing activity. These results indicate that GGR is active as long as it is anchored to membranes, even in the absence of LIL3. Subsequently, we addressed the question why the LHC motif is conserved in the LIL3 sequences. We modified the transmembrane domain of LIL3, which contains the LHC motif, by substituting its conserved amino acids (Glu-171, Asn-174, and Asp-189) with alanine. As a result, the Arabidopsis transgenic plants partly recovered the phytol-biosynthesizing activity. However, in these transgenic plants, the LIL3-GGR complexes were partially dissociated. Collectively, these results indicate that the LHC motif of LIL3 is involved in the complex formation of LIL3 and GGR, which might contribute to the GGR reaction.
authors.affiliation: From the Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan and.
authors.forename: Kaori
authors.initials: K
authors.lastname: Takahashi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takabayashi
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
authors.forename: Ryouichi
authors.initials: R
authors.lastname: Tanaka
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002734:Chlorophyll / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D015151:Immunoblotting; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D010836:Phytol / Q000378:metabolism; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D045342:Light-Harvesting Protein Complexes; C587631:light-harvesting-like protein 3, Arabidopsis; D002734:Chlorophyll; D010836:Phytol; D010088:Oxidoreductases; C110920:geranylgeranyl reductase
keywords: Arabidopsis; Chlorophyll; Chloroplast; Geranylgeranyl Reductase; Isoprenoid; Light-harvesting-like Protein; Plant Molecular Biology; Transgenic