EC Number   |
General Information |
Reference |
|---|
   1.3.7.3 | evolution |
the enzyme belongs to the the ferredoxin-dependent bilin reductase family. All members of the FDBR family are radical enzymes |
-, 724228 |
| 1.3.7.3 | metabolism |
during the biosynthesis of light-harvesting phycobilins in cyanobacteria, two members of the ferredoxin-dependent bilin reductases are involved in the reduction of the open-chain tetrapyrrole biliverdin IXa to the pink pigment phycoerythrobilin. The first reaction is catalyzed by 15,16-dihydrobiliverdin:ferredoxin oxidoreductase (PebA, EC 1.3.7.2) and produces the unstable intermediate 15,16-dihydrobiliverdin (DHBV). This intermediate is subsequently channeled to and converted by phycoerythrobilin:ferredoxin oxidoreductase to the final product phycoerythrobilin. An on-column assay employing immobilized enzyme in combination with UV-Vis and fluorescence spectroscopy reveals that both enzymes transiently interact and that transfer of the intermediate is facilitated by a significantly higher binding affinity of DHBV toward phycoerythrobilin:ferredoxin oxidoreductase (PebB). The intermediate DHBV is transferred via proximity channeling |
763020 |
| 1.3.7.3 | metabolism |
PebB, i.e. phycoerythrobilinPEB:ferredoxin oxidoreductase, acts in tandem with PebA, i.e. 15,16-DHBV:ferredoxin oxidoreductase, EC 1.3.7.2, which reduces biliverdin IXalpha at the C15-C16 double bond to produce 15,16-dihydrobiliverdin. Both enzymes function in close contact for metabolic channeling of 15,16-dihydrobiliverdin |
-, 724228 |
| 1.3.7.3 | metabolism |
phycobilins are light-harvesting pigments of cyanobacteria, red algae, and cryptophytes. The biosynthesis of phycoerythrobilin (PEB) is catalyzed by the subsequent action of two ferredoxin-dependent bilin reductases (FDBRs). 15,16-Dihydrobiliverdin (DHBV):ferredoxin oxidoreductase (PebA) catalyzes the two-electron reduction of biliverdin IXalpha to 15,16-DHBV, and PEB:ferredoxin oxidoreductase (PebB) reduces this intermediate further to PEB. The biosynthetic intermediate DHBV is transferred via proximity channeling to PEB:ferredoxin oxidoreductase (PebB). PebB is thus far the only FDBR member that cannot use BV as a substrate. In contrast the semireduced 15,16-DHBV is employed. Upon binding, this substrate is also protonated by the central aspartate. During the reaction, a second aspartate residue gets involved and likely serves as a proton donor for the proton coupled electron transfer to the A-ring of the tetrapyrrole molecule. This reaction catalyzed by PebB is a formal reduction of the 2,3,31,32-dien system of the A-ring of 15,16-DHBV |
-, 763264 |
| 1.3.7.3 | more |
structure comparisons of Synechococcus WH8020 PebA and Guillardia theta PebB, overview. The Asp-99/Asp-219 pair is structurally conserved in most FDBRs, while the corresponding residues are relevant for PebB, for PebA only the homologue of Asp99 (Asp84) is essential for catalytic activity. The homologue of Asp219 (Asp205) is not essential and is rotated out of the active site. PebB binds DHBV analogous to the binding of BV in PebA/PebS |
-, 763264 |
| 1.3.7.3 | more |
the highly conserved aspartate residues Asp107 and Asp231 are critical for the reduction. In addition to the importance of certain catalytic residues, the shape of the active site and consequently the binding of the substrate highly determines the catalytic properties |
-, 724228 |
| 1.3.7.3 | more |
the structures of PebB exhibit the typical alpha/beta/alpha-sandwich fold with a central antiparallel beta-sheet, flanked by alpha-helices. The open-chain tetrapyrrole substrate DHBV is bound in an unexpected flipped orientation within the canonical FDBR active site. Two central aspartate residues Asp99 and Asp219 as essential for catalytic activity. In addition, the conserved Arg215 plays a critical role in substrate specificity, binding orientation, and active site integrity. Because these critical residues are conserved within certain FDBRs displaying A-ring reduction activity, it is proposed that they present a conserved mechanism for this reaction. The flipped substrate-binding mode indicates that two-electron reducing FDBRs utilize the same primary site within the binding pocket and that substrate orientation is the determinant for Aor D-ring regiospecificity. Enzyme structure-function analysis, overview |
-, 763264 |
| 1.3.7.3 | physiological function |
phycobilins are light-harvesting pigments of cyanobacteria, red algae, and cryptophytes. The biosynthesis of phycoerythrobilin (PEB) is catalyzed by the subsequent action of two ferredoxin-dependent bilin reductases (FDBRs). 15,16-Dihydrobiliverdin (DHBV):ferredoxin oxidoreductase (PebA) catalyzes the two-electron reduction of biliverdin IXalpha to 15,16-DHBV, and PEB:ferredoxin oxidoreductase (PebB) reduces this intermediate further to PEB |
-, 763264 |
| 1.3.7.3 | physiological function |
phycobilisomes are composed of a core of allophycocyanin (APC) and radiating rods of phycocyanin (PC) and, depending on the species, phycoerythrin (PE) and phycoerythrocyanin (PEC), respectively. The individual phycobiliproteins are constituted of alpha- and beta-subunits building heterodimers and ultimately heterohexamers. Each subunit has between one and three covalently linked phycobilins bound. The two most abundant phycobilins in cyanobacteria are phycocyanobilin (PCB) and phycoerythrobilin (PEB) which are attached via conserved cysteine residues. During the biosynthesis of light-harvesting phycobilins in cyanobacteria, two members of the ferredoxin-dependent bilin reductases are involved in the reduction of the open-chain tetrapyrrole biliverdin IXa to the pink pigment phycoerythrobilin. The first reaction is catalyzed by 15,16-dihydrobiliverdin:ferredoxin oxidoreductase (PebA, UniProt ID Q02189) and produces the unstable intermediate 15,16-dihydrobiliverdin (DHBV). This intermediate is subsequently converted by phycoerythrobilin:ferredoxin oxidoreductase (PebB) to the final product phycoerythrobilin |
763020 |
