evolution
HemW-like proteins form a distinct phylogenetic clade. It contains the four cysteine residues of the radical S-adenosyl-L-methionine enzyme motif of CPDH enzymes, structure comparisons, overview. The fourth cysteine residue of the Fe-S cluster motif of Escherichia coli HemN, CX3CX2CXC, is replaced by phenylalanine in HemW and related proteins
evolution
in eukaryotes and some bacteria, oxidative decarboxylation of coproporphyrinogen III is performed by the oxygen-dependent CPO HemF,
EC 1.3.3.3. In most bacteria, the reaction is catalyzed by the oxygen-independent enzyme HemN. HemN belongs to the family of radical S-adenosyl-L-methionine enzymes. HemF and HemN are structurally completely unrelated and show different catalytic mechanisms, overview
evolution
the anaerobic [4Fe-4S] containing enzymes have been replaced in metabolic pathways by more efficient and stable aerobic versions as a response and adaptation to oxygen appearance on earth, with copper damages [4Fe-4S] cluster under anaerobiosis or limited oxygen tensionplaying a role in the selection pressure leading to the evolution of copper/oxygen tolerant enzymes, copper targets the 4Fe-4S clusters in the anaerobic enzymes
malfunction
excess copper in the copA- mutant, deficient for Cu+-ATPase CopA via transposon mutagenesis, results in a substantial decrease of the cytochrome c oxidase and the photosystem under microaerobic and anaerobic conditions together with the extrusion of coproporphyrin III. Enzyme CopA is required for the activity of cuproproteins in the purple bacterium Rubrivivax gelatinosus. CopA is not directly required for cytochrome c oxidase activity but is vital for copper tolerance. The Cu+-ATPase CtpA is required only for the activity of cuproproteins in the purple bacterium Rubrivivax gelatinosus
malfunction
mutation in Arabidopsis thaliana CPO-coding gene AtHEMN1 adversely affects silique length, ovule number, and seed set. T-DNA insertions in gene HEMN1 cause seed sterility. Athemn1 mutant alleles are transmitted via both male and female gametes, but homozygous mutants are never recovered. Plants carrying Athemn1 mutant alleles show defects in gametophyte development, including nonviable pollen and embryo sacs with unfused polar nuclei. Improper differentiation of the central cell leads to defects in endosperm development. Consequently, embryo development is arrested at the globular stage. Reactive oxygen species Accumulates around the central cell in the female gametophytes. The mutant phenotype is completely rescued by transgenic expression of AtHEMN1. Blockage of tetrapyrrole biosynthesis in the AtHEMN1 mutant leads to increased reactive oxygen species accumulation in anthers and embryo sacs. The accumulated reactive oxygen species disrupt mitochondrial function by altering their membrane polarity in floral tissues. The AtHEMN1 mutation prevents the fusion of polar nuclei in the female gametophyte and affects endosperm proliferation. T-DNA insertion mutant lines of Arabidopsis thaliana show bushy habit and short siliques. Cell specification is not affected in Athemn1-1 mutant embryo sacs. Phenotype, overview
malfunction
oxidized coproporphyrinogen III accumulates in a hemN2- mutant in Rubrivirax gelatinosus only under oxygen limited conditions
metabolism
genes hemH and hemW (hemN) show conjectured functions in heme metabolism
metabolism
the enzyme is involved in the O2-independent tetrapyrrole biosynthesis pathway, regulation overview
metabolism
the enzyme plays an important role in the tetrapyrrole biosynthesis pathway in plants, overview
more
a mutant Rubrivivax gelatinosus deficient in the Cu2+-ATPase CopA accumulates coproporphyrinogen III, excess copper affects the synthesis of tetrapyrroles, affecting the heme and chlorophyll containing complexes
