Teins (Arabidopsis Genome Initiative, 2000). Heme is synthesized in a multistep pathway, 5-aminolevulinic acid (ALA) being the earliest precursor. In plants ALA is used to form tetrapyrroles, which ?beside heme production – can also be used in three different pathways, leading to the production of phytochromobilin, the chromophore of the phytochrome family of red/far-red photoreceptors, to sirohaem, the cofactor of nitrite and sulphite reductases and to chlorophyll (Chl), the pigment responsible for harvesting and trapping light during photosynthesis [1,2]. All tetrapyrroles are synthesized in plastids. The terminal enzyme of the heme biosynthesis pathway is SC-1 ferrochelatase (protohaem ferrolyase, EC 4.99.1.1), catalyzing the insertion of ferrous iron into protoporphyrin IX. In mammalian cells ferrochelatase is located in mitochondria, as an integral component of the inner membrane with its active site on the matrix side [3]. Most higher plant genomes, however, contain two ferrochelatase genes, at different locations in the genome [4,5,6]. There is no clarity as to whether the different geneproducts are differentially targeted to chloroplasts and mitochondria [7]. Type I ferrochelatases can be imported into both mitochondria and chloroplasts [6,8], while type II ferrochelatases specifically have been found to be located in chloroplasts. Reports suggesting their mitochondrial localization have been disputed and the situation still remains unresolved [4,7,9,10]. The unicellular green alga Chlamydomonas reinhardtii contains both mitochondria and a chloroplast, but contains only one gene encoding a ferrochelatase, which is homologous to the Type II ferrochelatase found also in photosynthetic cyanobacteria [11]. Type II ferrochelatases of photosynthetic organisms contain a CAB motif, a conserved hydrophobic stretch that corresponds to the chlorophyll-binding domain in the first and third helices of light-harvesting antenna proteins in higher plants [12,13]. This CAB motif is only present in plant ferrochelatases that are expressed in photosynthetic tissues (Type II), but not in ferrochelatases that are expressed in non-photosynthetic tissues (Type I) [6,10]. The Type II enzyme is presumed to have evolved from the cyanobacterial ferrochelatase, which also possesses the Cterminal CAB motif [12]. The CAB motif is important for binding of chlorophyll a and b (CAB) to the higher plant light-harvesting complexes 18325633 and it is also found in the light-harvesting like proteins (Lil proteins). In the genome of the cyanobacterium Synechocystis sp. PCC6803 (hereafter Synechocystis 6803), five lil genes have been identified, coding for proteins with high similarity to the plantFerrochelatase Refolding and KineticsFigure 1. Schematic representation of recombinant His-FeCh, FeCh, His-FeChD347 and FeChD347 of Synechocystis 6803. The C-terminal CAB domain is exclusive to plastidic ferrochelatases of photosynthetic organisms, it is connected via a linker region to the catalytical domain (amino acids 1-324), where chelating of divalent metal ions into protoporphyrin IX takes place. N-terminal His6-tags have been added with the amino acid sequence Tunicamycin MGSSHHHHHHSSGLVPRGSH (for His-FeCh, cleavable by a thrombin protease) or MAHHHHHHVDDDDK (for His-FeChD347, cleavable by an enterokinase), respectively. doi:10.1371/journal.pone.0055569.glight-harvesting complexes [12]. Four genes encode the small CAB-like proteins (SCPs or high light induced proteins, HLIPs) referred to as.Teins (Arabidopsis Genome Initiative, 2000). Heme is synthesized in a multistep pathway, 5-aminolevulinic acid (ALA) being the earliest precursor. In plants ALA is used to form tetrapyrroles, which ?beside heme production – can also be used in three different pathways, leading to the production of phytochromobilin, the chromophore of the phytochrome family of red/far-red photoreceptors, to sirohaem, the cofactor of nitrite and sulphite reductases and to chlorophyll (Chl), the pigment responsible for harvesting and trapping light during photosynthesis [1,2]. All tetrapyrroles are synthesized in plastids. The terminal enzyme of the heme biosynthesis pathway is ferrochelatase (protohaem ferrolyase, EC 4.99.1.1), catalyzing the insertion of ferrous iron into protoporphyrin IX. In mammalian cells ferrochelatase is located in mitochondria, as an integral component of the inner membrane with its active site on the matrix side [3]. Most higher plant genomes, however, contain two ferrochelatase genes, at different locations in the genome [4,5,6]. There is no clarity as to whether the different geneproducts are differentially targeted to chloroplasts and mitochondria [7]. Type I ferrochelatases can be imported into both mitochondria and chloroplasts [6,8], while type II ferrochelatases specifically have been found to be located in chloroplasts. Reports suggesting their mitochondrial localization have been disputed and the situation still remains unresolved [4,7,9,10]. The unicellular green alga Chlamydomonas reinhardtii contains both mitochondria and a chloroplast, but contains only one gene encoding a ferrochelatase, which is homologous to the Type II ferrochelatase found also in photosynthetic cyanobacteria [11]. Type II ferrochelatases of photosynthetic organisms contain a CAB motif, a conserved hydrophobic stretch that corresponds to the chlorophyll-binding domain in the first and third helices of light-harvesting antenna proteins in higher plants [12,13]. This CAB motif is only present in plant ferrochelatases that are expressed in photosynthetic tissues (Type II), but not in ferrochelatases that are expressed in non-photosynthetic tissues (Type I) [6,10]. The Type II enzyme is presumed to have evolved from the cyanobacterial ferrochelatase, which also possesses the Cterminal CAB motif [12]. The CAB motif is important for binding of chlorophyll a and b (CAB) to the higher plant light-harvesting complexes 18325633 and it is also found in the light-harvesting like proteins (Lil proteins). In the genome of the cyanobacterium Synechocystis sp. PCC6803 (hereafter Synechocystis 6803), five lil genes have been identified, coding for proteins with high similarity to the plantFerrochelatase Refolding and KineticsFigure 1. Schematic representation of recombinant His-FeCh, FeCh, His-FeChD347 and FeChD347 of Synechocystis 6803. The C-terminal CAB domain is exclusive to plastidic ferrochelatases of photosynthetic organisms, it is connected via a linker region to the catalytical domain (amino acids 1-324), where chelating of divalent metal ions into protoporphyrin IX takes place. N-terminal His6-tags have been added with the amino acid sequence MGSSHHHHHHSSGLVPRGSH (for His-FeCh, cleavable by a thrombin protease) or MAHHHHHHVDDDDK (for His-FeChD347, cleavable by an enterokinase), respectively. doi:10.1371/journal.pone.0055569.glight-harvesting complexes [12]. Four genes encode the small CAB-like proteins (SCPs or high light induced proteins, HLIPs) referred to as.