Light Stress-Induced One-Helix Protein of the Chlorophylla/b-Binding Family Associated with Photosystem I

Abstract

The superfamily of light-harvesting chlorophyll a/b-binding (Lhc) proteins in higher plants and green algae is composed of more than 20 different antenna proteins associated either with photosystem I (PSI) or photosystem II (PSII). Several distant relatives of this family with conserved chlorophyll-binding residues and proposed photoprotective functions are induced transiently under various stress conditions. Whereas "classical" Lhc proteins contain three-transmembrane ␣-helices, their distant relatives span the membrane with between one and four transmembrane segments. Here, we report the identification and isolation of a novel member of the Lhc family from Arabidopsis with one predicted transmembrane ␣-helix closely related to helix I of Lhc protein from PSI (Lhca4) that we named Ohp2 (for a second one-helix protein of Lhc family described from higher plants). We showed that the Ohp2 gene expression is triggered by light stress and that the Ohp2 transcript and protein accumulated in a light intensity-dependent manner. Other stress conditions did not up-regulate the expression of the Ohp2 gene. Localization studies revealed that Ohp2 is associated with PSI under low-or high-light conditions. Because all stress-induced Lhc relatives reported so far were found in PSII, we propose that the accumulation of Ohp2 might represent a novel photoprotective strategy induced within PSI in response to light stress.The superfamily of light-harvesting chlorophyll a/b-binding (Lhc) proteins in higher plants and green algae is composed of more than 20 different members associated with photosystem I (PSI) or photosystem II (PSII). The primary function of these proteins is the absorption of light through chlorophyll excitation and the transfer of the absorbed energy to photochemical reaction centers (Green and Durnford, 1996). On the basis of the three-dimensional structure determined at 3.4-Å resolution for one member of the Lhc family from higher plants (Kü hlbrandt et al., 1994), it was proposed that all Lhc proteins in higher plants and green algae have three transmembrane ␣-helices, where helices I and III are evolutionarily related to each other and held together by ion pairs formed by charged residues.In the past few years, several distant relatives of Lhc protein family with conserved chlorophyllbinding residues and a transient expression pattern related to various stress conditions have been described from higher plants, algae, or cyanobacteria (Adamska, 2001). These distant relatives include the four-helix PsbS protein of PSII (Funk, 2001) and a subfamily of proteins called early light-induced proteins (Elips; Adamska, 1997Adamska, , 2001 Montané and Kloppstech, 2000). The Elip subfamily consists of three-helix Elips, two-helix stress-enhanced proteins (Seps), and one-helix proteins (Ohps) also called high-light-induced proteins (Hlips) or small chlorophyll a/b-binding-like proteins (Scps) in prokaryotic organisms (Adamska, 2001). All Elip subfamily members are short-lived proteins (Meyer and Kloppstech, 1984; Grim...

Cyanobacterial Small Chlorophyll-binding Protein ScpD (HliB) Is Located on the Periphery of Photosystem II in the Vicinity of PsbH and CP47 Subunits

“…The specific interaction of ScpDHis with PSII was further confirmed by the observation that in the absence of PSII, the ScpDHis protein was present in the form of small protein complexes. This also indicated that ScpDHis does not interact with other large thylakoid membrane complexes, particularly PSI, as was shown recently for the plant SCP homologue OHP (36). We also succeeded in a more detailed localization of ScpDHis within PSII as we detected the protein in the complex of CP47 and PsbH that accumulates at low levels in the strain unable to assemble PSII complexes because of the missing cytochrome b 559 (Fig.…”

Abundantly and Rarely Expressed Lhc Protein Genes Exhibit Distinct Regulation Patterns in Plants

“…When the Arabidopsis genome sequence appeared, it was apparent that two of the proposed Lhcb2 genes (Jansson, 1999) were actually two alleles of the same gene, resulting in renaming the Lhcb2.4 (At3g27690) gene to Lhcb2.3 (Legen et al, 2001;Andersson et al, 2003a). On the other hand, a gene coding for an additional OHP that initially escaped detection was subsequently characterized (Andersson et al, 2003b), keeping the number of known genes at 30 in Arabidopsis. In poplar the Lhc supergene family is slightly larger with 39 Lhc genes identified (Table I).…”

“…The Lhc supergene family of higher plants also contains genes coding for proteins that exhibit sequence similarity to the Lhc proteins, namely, the four-helix protein PsbS and the light-harvesting-like (LIL) proteins. So far, six different classes of Lil genes have been identified (Jansson, 1999;Heddad and Adamska, 2000;Andersson et al, 2003b). The Lil1 genes code for the three-helix early light-inducible proteins (ELIPs), two types of one-helix proteins (OHPs) are encoded by Lil2 (OHP1) and Lil6 (OHP2), and two types of stressenhanced proteins (SEPs) are encoded by Lil4 (SEP1) and Lil5 (SEP2).…”

“…However, biochemical characterizations have strongly indicated interactions for some of them, e.g. PsbS with PSII (Funk et al, 1995) or OHP2 with PSI (Andersson et al, 2003b). Therefore, their absence in the structures might be due to the fact that their interactions with the photosynthetic reaction centers are less strong or temporarily limited, but they also might have a function more independently from a close association with the reaction centers.…”

LIL3, a light-harvesting-like protein, plays an essential role in chlorophyll and tocopherol biosynthesis

“…OHP, SEP, and ELIP proteins are proposed to be involved in protection against excessive light. The expression of the genes for these proteins is induced under strong illumination (15)(16)(17)(18)(19). In addition, it has also been suggested that ELIP functions as a repressor of chlorophyll biosynthesis (20).…”