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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