Esterifying alcohols in the chlorophylls of purple photosynthetic bacteria. New chlorophyll, bacteriochlorophyll (gg), all-trans-geranylgeranyl bacteriochlorophyllide a

Katz, Joseph; Strain, H. H.; Harkness, A.L.; Studier, Martin H.; Svec, Walter A.; Janson, Thomas R.; Cope, B. T.

doi:10.1021/ja00777a054

Cited by 73 publications

(31 citation statements)

References 2 publications

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“…The majority (approximately 68%) was BchlaGG, which occurs as a minor constituent in wild-type R. sphaeroides cells, particularly those undergoing rapid growth and pigment biosynthesis [ Fig. 4B, trace (v)] (33), and is also the principal Bchl pigment of Rhodospirillum rubrum (21). The remainder consisted of BchlaDHGG (7.3%) and BchlaTHGG (13.2%), which are also present as minor constituents in wild-type R. sphaeroides [ Fig.…”

Section: Resultsmentioning

confidence: 99%

Physical Mapping of bchG , orf427 , and orf177 in the Photosynthesis Gene Cluster of Rhodobacter sphaeroides : Functional Assignment of the Bacteriochlorophyll Synthetase Gene

2000

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The purple photosynthetic bacterium Rhodobacter sphaeroides has within its genome a cluster of photosynthesis-related genes approximately 41 kb in length. In an attempt to identify genes involved in the terminal esterification stage of bacteriochlorophyll biosynthesis, a previously uncharacterized 5-kb region of this cluster was sequenced. Four open reading frames (ORFs) were identified, and each was analyzed by transposon mutagenesis. The product of one of these ORFs, bchG, shows close homologies with (bacterio)chlorophyll synthetases, and mutants in this gene were found to accumulate bacteriopheophorbide, the metal-free derivative of the bacteriochlorophyll precursor bacteriochlorophyllide, suggesting that bchG is responsible for the esterification of bacteriochlorophyllide with an alcohol moiety. This assignment of function to bchG was verified by the performance of assays demonstrating the ability of BchG protein, heterologously synthesized in Escherichia coli, to esterify bacteriochlorophyllide with geranylgeranyl pyrophosphate in vitro, thereby generating bacteriochlorophyll. This step is pivotal to the assembly of a functional photosystem in R. sphaeroides, a model organism for the study of structure-function relationships in photosynthesis. A second gene, orf177, is a member of a large family of isopentenyl diphosphate isomerases, while sequence homologies suggest that a third gene, orf427, may encode an assembly factor for photosynthetic complexes. The function of the remaining ORF, bchP, is the subject of a separate paper (H. Addlesee and C. N. Hunter, J. Bacteriol. 181:7248-7255, 1999). An operonal arrangement of the genes is proposed.A rigorous program of sequencing combined with mutational and biochemical analysis has revealed within the genome of the purple bacterium Rhodobacter sphaeroides the presence of a 41-kb gene cluster holding virtually all of the loci directly responsible for its photosynthetic ability ( Fig. 1) (11,12,27), including those encoding enzymes of the bacteriochlorophyll (Bchl) biosynthesis pathway. The Bchla molecules of R. sphaeroides are esterified with phytol, a C 20 isoprenoid alcohol, which constitutes 30% of the total molecular weight and also greatly influences the molecules' properties by investing them with much of their hydrophobicity. The structural data for bacterial reaction center and light-harvesting complexes (13,15,26) enable the conformations adopted by many of the phytol chains to be examined in atomic detail. In light-harvesting complex 2 (LH2), it appears that the close intertwining of the phytol tails of the B800 and B850 Bchls, along with the carotenoid chains, imparts a significant amount of stability to the complex. Indeed, it appears that the addition of the alcohol moiety, the final act of Bchl biosynthesis in this organism, is a crucial determinant of the assembly of the entire photosynthetic apparatus (references 9 and 31 and this study). The tails also play a major role in controlling the orientation of the transition dipoles of the tetrapyrrole r...

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Section: Resultsmentioning

confidence: 99%

Physical Mapping of bchG , orf427 , and orf177 in the Photosynthesis Gene Cluster of Rhodobacter sphaeroides : Functional Assignment of the Bacteriochlorophyll Synthetase Gene

2000

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“…This revealed a ring structure composed of 16 ␣␤ heterodimers, the central hole of which is now known to be occupied by the RC (35). The Bchla with which these complexes are assembled is esterified with the C 20 isoprenoid alcohol geranylgeraniol (GG) (20). In this respect, Rhodospirillum rubrum again differs from other purple bacteria, including the well-characterized Rhodobacter species Rhodobacter sphaeroides and Rhodobacter capsulatus.…”

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confidence: 99%

Rhodospirillum rubrum Possesses a Variant of the bchP Gene, Encoding Geranylgeranyl-Bacteriopheophytin Reductase

Addlesee

Hunter

2002

J Bacteriol

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The bchP gene product of Rhodobacter sphaeroides is responsible for the reduction of the isoprenoid moiety of bacteriochlorophyll (Bchl) from geranylgeraniol (GG) to phytol; here, we show that this enzyme also catalyzes the reduction of the isoprenoid moiety of bacteriopheophytin (Bphe). In contrast, we demonstrate that a newly identified homolog of this gene in Rhodospirillum rubrum encodes an enzyme, GG-Bphe reductase, capable of reducing the isoprenoid moiety of Bphe only. We propose that Rhodospirillum rubrum is a naturally occurring bchP mutant and that an insertion mutation may have been the initial cause of a partial loss of function. Normal BchP function can be restored to Rhodospirillum rubrum, creating a new transconjugant strain possessing Bchl esterified with phytol. We speculate on the requirement of Rhodospirillum rubrum for phytylated Bphe and on a potential link between the absence of LH2 and of phytylated Bchl from the wild-type bacterium. The identification of a second role for the fully functional BchP in catalyzing the synthesis of phytylated Bphe strongly suggests that homologs of this enzyme may be similarly responsible for the synthesis of phytylated pheophytin in organisms possessing photosystem 2. In addition to bchP, other members of a photosynthesis gene cluster were identified in Rhodospirillum rubrum, including a bchG gene, demonstrated to encode a functional Bchl synthetase by complementation of a Rhodobacter sphaeroides mutant.

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“…Bacteriochlorophyllide u (ull-trans)-geranylgeranyl ester has also been rcportcd, and called bacteriochlorophyll gg [30].…”

Section: O6mentioning

confidence: 99%

IUPAC‐IUB Joint Commission on Biochemical Nomenclature (JCBN) Nomenclature of Tetrapyrroles Recommendations 1978

Merritt¹,

Loening²

1980

European Journal of Biochemistry

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Esterifying alcohols in the chlorophylls of purple photosynthetic bacteria. New chlorophyll, bacteriochlorophyll (gg), all-trans-geranylgeranyl bacteriochlorophyllide a

Cited by 73 publications

References 2 publications

Physical Mapping of bchG , orf427 , and orf177 in the Photosynthesis Gene Cluster of Rhodobacter sphaeroides : Functional Assignment of the Bacteriochlorophyll Synthetase Gene

Physical Mapping of bchG , orf427 , and orf177 in the Photosynthesis Gene Cluster of Rhodobacter sphaeroides : Functional Assignment of the Bacteriochlorophyll Synthetase Gene

Rhodospirillum rubrum Possesses a Variant of the bchP Gene, Encoding Geranylgeranyl-Bacteriopheophytin Reductase

IUPAC‐IUB Joint Commission on Biochemical Nomenclature (JCBN) Nomenclature of Tetrapyrroles Recommendations 1978

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