The terminal enzymes of (bacterio)chlorophyll biosynthesis

Abstract

(Bacterio)chlorophylls are modified tetrapyrroles that are used by phototrophic organisms to harvest solar energy, powering the metabolic processes that sustain most of the life on Earth. Biosynthesis of these pigments involves enzymatic modification of the side chains and oxidation state of a porphyrin precursor, modifications that differ by species and alter the absorption properties of the pigments. (Bacterio)chlorophylls are coordinated by proteins that form macromolecular assemblies to absorb light and transfer excitation energy to a special pair of redox-active (bacterio)chlorophyll molecules in the photosynthetic reaction centre. Assembly of these pigment–protein complexes is aided by an isoprenoid moiety esterified to the (bacterio)chlorin macrocycle, which anchors and stabilizes the pigments within their protein scaffolds. The reduction of the isoprenoid ‘tail’ and its addition to the macrocycle are the final stages in (bacterio)chlorophyll biosynthesis and are catalysed by two enzymes, geranylgeranyl reductase and (bacterio)chlorophyll synthase. These enzymes work in conjunction with photosynthetic complex assembly factors and the membrane biogenesis machinery to synchronize delivery of the pigments to the proteins that coordinate them. In this review, we summarize current understanding of the catalytic mechanism, substrate recognition and regulation of these crucial enzymes and their involvement in thylakoid biogenesis and photosystem repair in oxygenic phototrophs.

Absolute quantification of cellular levels of photosynthesis-related proteins in Synechocystis sp. PCC 6803

“…The final two steps in Chl biosynthesis can occur in either order (Soll et al 1983 ; Proctor et al 2022a ). Geranylgeranyl reductase (ChlP) catalyses the hydrogenation of three C = C double bonds on the C 20 isoprenoid geranylgeranyl pyrophosphate (GGPP) to produce phytyl pyrophosphate.…”

“…Alternatively, ChlG can first attach a geranylgeranyl group to Chlide for subsequent reduction to phytyl by ChlP. ChlP is probably active on the cytosplasmic surface of the TM, whereas ChlG is predicted to be membrane-intrinsic (Gaubier et al 1995 ) with up to nine TMHs (Proctor et al 2022a ). ChlP was quantified at 1150–1850 cpc, the sixth Chl biosynthesis pathway component to fall into the shared 1150–3550 cpc range indicated by horizontal dashed lines in Fig.…”

Chlorophyll a Synthesis in Rhodobacter sphaeroides by Chlorophyll Synthase of Nicotiana tabacum

“…Broadening the absorption spectra of PS organisms may improve the efficiency of light utilization [ 4 ]. Recently, heterologous pigments, such as BChl b P [ 5 , 6 ] and farnesylated BChl g (BChl g F ) [ 7 ], were produced in metabolically-engineered R. sphaeroides under microoxic conditions.…”

Engineering Chlorophyll, Bacteriochlorophyll, and Carotenoid Biosynthetic Pathways in Escherichia coli

“…The C7C8 double bond of Chlide a is reduced by the nitrogenase-like enzyme chlorophyllide a oxidoreductase (COR, BchXYZ), producing 3-vinyl bacteriochlorophyllide a (3V BChlide a ). , COR also has latent DVR activity and thus is able to use DV Chlide a as substrate to form 3V BChlide a . , The 3-vinyl group undergoes hydroxylation by 3V BChlide a hydratase (BchF) to form a hydroxyethyl (HE) group, which is oxidized by 3HE BChlide a dehydrogenase (BchC) to form an acetyl group, thus producing BChlide a . Alternative reaction sequences are possible in which the COR step is preceded by the formation of the 3-HE or 3-acetyl from the 3-vinyl group. , Chl a and BChl a share the final biosynthetic steps for attachment of a phytol moiety to the macrocycle (Figure A). In the Chl a branch, Chlide a is esterified with geranylgeranyl pyrophosphate (GGPP) by Chl synthase (ChlG).…”