Magnesium-protoporphyrin IX monomethyl ester [oxidative] cyclase (IPR008434)

Short name: AcsF

Overlapping homologous superfamilies

Family relationships



This family represents the oxidative cyclase responsible for forming the distinctive E-ring of the chlorin ring system under aerobic conditions [PMID: 11790744]. This enzyme is believed to utilise a binuclear iron centre and molecular oxygen. There are two isoforms of this enzyme in some plants and cyanobacteria, which are differentially regulated based on the levels of copper and oxygen [PMID: 10811605, PMID: 11910013]. This step is essential in the biosynthesis of both bacteriochlorophyll and chlorophyll under aerobic conditions (a separate enzyme, BchE, acts under anaerobic conditions). This enzyme is found in plants, cyanobacteria and other photosynthetic bacteria.

CRD1 (AcsF) is required for the maintenance of photosystem I and its associated light-harvesting complexes in copper-deficient (-Cu) and oxygen-deficient (-O(2)) Chlamydomonas reinhardtii cells and is localised to the thylakoid membrane. The family also contains the Rhodocyclus gelatinosus (Rhodopseudomonas gelatinosa or Rubrivivax gelatinosus) AcsF protein, which codes for a conserved, putative binuclear iron-cluster-containing protein involved in aerobic oxidative cyclization of Mg-protoporphyrin IX monomethyl ester. AcsF and homologs have a leucine zipper and two copies of the conserved glutamate and histidine residues predicted to act as ligands for iron in the Ex(29-35)DExRH motifs. Several homologs of AcsF are found in a wide range of photosynthetic organisms, including Chlamydomonas reinhardtii Crd1 and Pharbitis nil PNZIP, suggesting that this aerobic oxidative cyclization mechanism is conserved from bacteria to plants [PMID: 11790744].

GO terms

Biological Process

GO:0015995 chlorophyll biosynthetic process
GO:0015979 photosynthesis

Molecular Function

GO:0048529 magnesium-protoporphyrin IX monomethyl ester (oxidative) cyclase activity
GO:0046872 metal ion binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.