Literature summary for 1.14.13.81 extracted from

Stuart, D.; Sandstroem, M.; Youssef, H.M.; Zakhrabekova, S.; Jensen, P.E.; Bollivar, D.W.; Hansson, M.
Aerobic barley Mg-protoporphyrin IX monomethyl ester cyclase is powered by electrons from ferredoxin (2020), Plants (Basel), 9, 1157 .

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Cloned(Commentary)

Cloned (Comment)	Organism
gene Xantha-I, recombinant expression of active XanL strictly requires co-expression with an additional protein, Ycf54, recombinant expression of His-tagegd XanL and Ycf54 in Escherichia coli strain Artic Express (DE3)	Hordeum vulgare

Inhibitors

Inhibitors	Comment	Organism	Structure
additional information	assays performed with barley extract are inhibited by antibodies raised against ferredoxin and ferredoxin-NADPH oxidoreductase (FNR)	Hordeum vulgare

Localization

Localization	Comment	Organism	GeneOntology No.	Textmining
chloroplast membrane	membrane-bound	Hordeum vulgare	31969	-
etioplast	-	Hordeum vulgare	9513	-

Metals/Ions

Metals/Ions	Comment	Organism	Structure
Fe2+	required, the aerobic cyclase belongs to the family of diiron carboxylate-bridged proteins characterized by the iron-binding motif E-Xn-E-X-X-H-Xn-E-Xn-E-X-X-H	Hordeum vulgare
Mg2+	required	Hordeum vulgare

Natural Substrates/ Products (Substrates)

Natural Substrates	Organism	Comment (Nat. Sub.)	Natural Products	Comment (Nat. Pro.)	Rev.	Reac.
magnesium-protoporphyrin IX 13-monomethyl ester + 3 NADPH + 3 H+ + 3 O2	Hordeum vulgare	overall reaction	3,8-divinyl protochlorophyllide a + 3 NADP+ + 5 H2O	-	?

Organism

Organism	UniProt	Comment	Textmining
Hordeum vulgare	Q5EFU4	cv. Bonus	-

Reaction

Reaction	Comment	Organism	Reaction ID
magnesium-protoporphyrin IX 13-monomethyl ester + 3 NADPH + 3 H+ + 3 O2 = 3,8-divinyl protochlorophyllide a + 3 NADP+ + 5 H2O	overall reaction, reaction mechanism of the aerobic cyclase reaction, overview. The cyclase reaction is a six-electron redox reaction suggested to proceed via beta-hydroxy and beta-keto intermediates. The electrons are provided by Fd. NADPH can be used as the source of electrons transferred to ferredoxin (Fd) via ferredoxin-NADPH oxidoreductase (FNR). In green tissue, Fd can also be reduced by photosystem I	Hordeum vulgare	a

Substrates and Products (Substrate)

Substrates	Comment Substrates	Organism	Products	Comment (Products)	Rev.	Reac.
magnesium-protoporphyrin IX 13-monomethyl ester + 3 NADPH + 3 H+ + 3 O2	overall reaction	Hordeum vulgare	3,8-divinyl protochlorophyllide a + 3 NADP+ + 5 H2O	-	?
additional information	in vitro cyclase activity is obtained with recombinant XanL in combination with ferredoxin (Fd) and ferredoxin-NADPH oxidoreductase (FNR). Fd and FNR are plastid-localized redox components. Enzymatic assays combining spinach Fd and FNR with XanL[coYcf54] show high activity	Hordeum vulgare	?	-	-

Synonyms

Synonyms	Comment	Organism
CRD1	-	Hordeum vulgare
Mg-protoporphyrin IX monomethyl ester cyclase	-	Hordeum vulgare
MPE cyclase	-	Hordeum vulgare
XanL	-	Hordeum vulgare
Xantha-l	-	Hordeum vulgare

Temperature Optimum [°C]

Temperature Optimum [°C]	Temperature Optimum Maximum [°C]	Comment	Organism
30	-	assay at	Hordeum vulgare

pH Optimum

pH Optimum Minimum	pH Optimum Maximum	Comment	Organism
8.1	-	assay at	Hordeum vulgare

Cofactor

Cofactor	Comment	Organism	Structure
Ferredoxin	the MPE cyclase is a ferredoxin-dependent enzyme	Hordeum vulgare
NADPH	-	Hordeum vulgare

General Information

General Information	Comment	Organism
evolution	two distinct enzymes have been identified that catalyze the cyclase reaction, originally distinguished by the source of the incorporated oxygen. The enzyme that catalyzes the cyclase reaction in the absence of molecular oxygen (anaerobic) derives the oxygen from water and is encoded by bchE in facultative photosynthetic bacteria like Rhodobacter sphaeroides. The anaerobic enzyme functions as a hydratase, whereas the aerobic cyclase is an oxygenase. The aerobic cyclase belongs to the family of diiron carboxylate-bridged proteins characterized by the iron-binding motif E-Xn-E-X-X-H-Xn-E-Xn-E-X-X-H. The cyclase activity requires both additional soluble and membrane-bound fractions	Hordeum vulgare
metabolism	in the first unique step of the chlorophyll biosynthetic pathway, Mg2+ is inserted into protoporphyrin IX. Subsequently, a methyl group is transferred to the carboxyl group of the propionate on the C ring of Mg-protoporphyrin IX, generating Mg-protoporphyrin IX monomethyl ester (MPE), which is the substrate of the MPE cyclase. The cyclase catalyzes the formation of the isocyclic E ring by insertion of oxygen and attaching the methylated propionate to the methene bridge between pyrrole rings C and D, forming protochlorophyllide. Chlorophyll is obtained after additional reactions involving a light-dependent oxidation of protochlorophyllide to chlorophyllide, reduction of the vinyl group on the B ring, and, finally, addition of a polyisoprene tail	Hordeum vulgare
physiological function	the Xantha-l gene product (XanL) is a membrane-bound diiron monooxygenase, which requires additional soluble and membrane-bound components for its activity. The enzyme XanL is a Mg-protoporphyrin IX monomethyl ester cyclase involved in the formation of the isocyclic E-ring characteristic of chlorophylls. The MPE cyclase is a ferredoxin-dependent enzyme. Ferredoxin is part of the photosynthetic electron-transport chain, which suggests that the cyclase reaction might be connected to photosynthesis under light conditions	Hordeum vulgare

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Release 2023.1 (January 2023)