GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000041

Gene Ontology annotation based on UniPathway vocabulary mapping

GO_REF:0000118

TreeGrafter-generated GO annotations

file:genes/RHOCB/bchE/bchE-uniprot.txt

UniProt record for Rhodobacter capsulatus bchE (P26168)

PMID:8158642

Directed mutational analysis of bacteriochlorophyll a biosynthesis in Rhodobacter capsulatus.

Twelve photosynthesis-gene-cluster reading frames were disrupted by directed mutagenesis; seven disruptions abolished bacteriochlorophyll biosynthesis with accumulation of specific Mg-tetrapyrrole intermediates.

"The results of this analysis demonstrate that mutations constructed in seven open reading frames resulted in a loss of bacteriochlorophyll biosynthesis, concomitant with the accumulation of specific intermediates in the Mg-tetrapyrrole biosynthetic pathway."

PMID:2203738

Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway.

Disruption of photosynthesis-gene-cluster reading frame F1025, later named bchE, blocked conversion of magnesium-protoporphyrin monomethyl ester to protochlorophyllide.

"Three open reading frames in the Rhodobacter capsulatus photosynthesis gene cluster, designated F0, F108, and F1025, were disrupted by site-directed mutagenesis. Mutants bearing insertions in these reading frames were defective in converting protoporphyrin IX to magnesium-protoporphyrin monomethyl ester, protochlorophyllide to chlorophyllide a, and magnesium-protoporphyrin monomethyl ester to protochlorophyllide, respectively."

PMID:10841582

Anaerobic chlorophyll isocyclic ring formation in Rhodobacter capsulatus requires a cobalamin cofactor.

MPE cyclase activity in R. capsulatus has an absolute requirement for vitamin B12 or adenosylcobalamin, shown in a B12-auxotrophic mutant under inhibited protein synthesis, so the cofactor acts directly on the cyclase reaction.

"Fig. 5 C shows that mutant MPE cyclase activity has an absolute demand for exogenous B 12 or AdCob. This experiment shows that a cobalamin cofactor acts directly on the cyclase reaction."
MPE accumulates in bchE transposon mutants of R. capsulatus, which is the basis for assigning MPE cyclase function to the bchE product.

"MPE accumulates in transposon mutants of the Rhodobacter capsulatus bchE gene, suggesting that the encoded protein is required for MPE-cyclase activity"
The iron-sulfur centre of BchE was proposed from a cysteine-spacing resemblance to biotin synthase, not demonstrated, in this work.

"This cysteine arrangement resembles somewhat an iron-sulfur center as found in biotin synthase"
The experiments were performed in R. capsulatus strain 37b4 and its derivatives, not in strain SB1003 from which P26168 derives.

"Cell growth of capsule-less wild-type R. capsulatus 37b4"

PMID:33211085

Mg-protoporphyrin IX monomethyl ester cyclase from Rhodobacter capsulatus: radical SAM-dependent synthesis of the isocyclic ring of bacteriochlorophylls.

Site-directed mutagenesis and in vivo complementation of R. capsulatus BchE identified Cys204, Cys208 and Cys211 as the [4Fe-4S] cluster ligands, Phe210, Glu308 and Lys320 for SAM, and Asp248, Glu249, Leu29, Thr71 and Val97 for cobalamin.

"Potential ligands of the [4Fe-4S] cluster (Cys204, Cys208, Cys211), of SAM (Phe210, Glu308 and Lys320) and of the proposed cobalamin cofactor (Asp248, Glu249, Leu29, Thr71, Val97) were identified."
Subcellular fractionation of R. capsulatus placed BchE on the membrane and showed that activity additionally requires a heat-sensitive soluble component of about 3-10 kDa.

"Subcellular fractionation experiments revealed that membrane-localized BchE requires an additional, heat-sensitive cytosolic component for activity."
The oxo oxygen installed by R. capsulatus BchE derives from water, shown by H2(18)O isotope label transfer onto the C13(1)-oxo group of protochlorophyllide.

"We established a spectroscopic in vitro activity assay which was subsequently validated by HPLC analyses and H218O isotope label transfer onto the carbonyl-group (C-131-oxo) of the isocyclic ring of Pchlide."

PMID:42748141

Isolation and in vitro characterization of BchE, the cobalamin-dependent anaerobic magnesium protoporphyrin IX monomethylester cyclase.

R. capsulatus encodes no aerobic AcsF cyclase, so all protochlorophyllide in this organism is made by BchE.

"R. capsulatus does not utilize AcsF, so all production of PChlide must originate through the action of BchE."
Purified BchE binds both cobalamin and a [Fe4S4] cluster, confirmed by UV-visible and EPR spectroscopy, and turns over MPE to protochlorophyllide in vitro with chemical or ferredoxin reductants.

"The enzyme was purified anaerobically and characterized by UV-Vis and electron paramagnetic resonance spectroscopy to confirm the presence of Cbl and a [Fe4S4] cluster."
The reconstituted enzyme was the Rubrivivax pictus ortholog; of BchE homologs from eight organisms only three were soluble and only the R. pictus protein was catalytically productive.

"we attempted heterologous expression and purification of BchE homologs from eight different organisms; only three yielded any soluble protein, and of these, only BchE from Rubrivivax pictum catalyzed the formation of PChlide."
Soluble R. capsulatus BchE was purified but produced only the off-pathway 575 nm species and no protochlorophyllide, and was not rescued by the candidate partner ferredoxin RcFdxA.

"In our attempts to obtain soluble BchE constructs, we also purified BchE from R. capsulatus and R. gelatinosus. Neither of these enzymes produced the PChlide product and could only form the 575 species using Ti(III)citrate with no activity using ferredoxins."