Table 2 Detailed comparison of different heme-/siroheme-binding ferredoxin α + β barrel families
From: Evolutionary relationships between heme-binding ferredoxin α + β barrels
IsdG homologs | OxdA | Cld/DyP/EfeB/HemQ | Siroheme decarboxylase | |
|---|---|---|---|---|
Number of heme/siroheme per barrel | 2 (IsdG/IsdI, PDB identifier 2ZDO/2ZDP) (1/monomer) | 1 (in C-terminal ferredoxin-like domain) | 1 (between the two ferredoxin-like domains) | |
4 (MhuD, PDB identifier 3HX9) (2/monomer) | ||||
1 (HmoB, PDB identifier 4OZ5) (1 in C-terminal ferredoxin-like domain) | ||||
Heme/siroheme binding pocket | Cleft of the ferredoxin-like domain | Barrel cavity | ||
Function of heme/siroheme | Substrate | Cofactor | Cofactor, Product (HemQ) | Metabolic intermediate |
Shape of heme/siroheme | Ruffled | Ruffled | Planar | Ruffled siroheme |
Location of the proximal His-axial residue | α2 of ferredoxin-like domain (α3 in the contiguous duplicated domains in HmoB) | α2 of the ferredoxin-like domain (α4 in the contiguous duplicated domains). These are spatially not equivalent to α2 of IsdG homologs. | α1 of the ferredoxin-like domain (α3 in the contiguous duplicated domains). These are spatially equivalent to OxdA. | β2 of the ferredoxin-like domain of chain A in D. desulfuricans. β6 of the contiguous duplicated domains of the barrel in H. thermophilus |
Distal heme residue | Asparagine | Histidine | Arginine | Histidine |