SUPERFAMILY 1.73 HMM library and genome assignments server


Cytochrome b5-like heme/steroid binding domain superfamily

SCOP classification
Root:   SCOP hierarchy in SUPERFAMILY [ 0] (11)
Class:   Alpha and beta proteins (a+b) [ 53931] (334)
  Mainly antiparallel beta sheets (segregated alpha and beta regions)
Fold:   Cytochrome b5-like heme/steroid binding domain [ 55855]
  beta-alpha-beta(2)-alpha(1,2)-(beta)-alpha(2)-beta; 3 layers: a/b/a; antiparallel beta-sheet, order: 1532(4)
Superfamily:   Cytochrome b5-like heme/steroid binding domain [ 55856] (2)
Families:   Cytochrome b5 [ 55857] (4)
  Steroid-binding domain [ 103222]


Superfamily statistics
Genomes (319) UniProt 15.0 PDB chains (SCOP 1.73)
Domains 4,249 2,328 33
Proteins 4,198 2,282 33


Functional annotation
General category Metabolism
Detailed category E- transfer

Function annotation of SCOP domain superfamilies
InterPro annotation
Cross references IPR001199 SSF55856 Protein matches
Abstract Cytochromes b5 are ubiquitous electron transport proteins found in animals, plants and yeasts [PubMed2752049]. The microsomal and mitochondrial variants are membrane-bound, while those from erythrocytes and other animal tissues are water-soluble [PubMed4030743, PubMed8439576].

The 3D structure of bovine cyt b5 is known, the fold belonging to the alpha+beta class, with 5 strands and 5 short helices forming a framework for supporting a central haem group [PubMed1167544]. The cytochrome b5 domain is similar to that of a number of oxidoreductases, such as plant and fungal nitrate reductases, sulphite oxidase, yeast flavocytochrome b2 (L-lactate dehydrogenase) and plant cyt b5/acyl lipid desaturase fusion protein.


InterPro database

PDBeMotif information about ligands, sequence and structure motifs
Cross references PDB entries
Ligand binding statistics
Nucleic-acid binding statistics
Occurrence of secondary structure elements
Occurrence of small 3D structural motifs

PDBeMotif resource

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Internal database links

Browse genome assignments for this superfamily. The SUPERFAMILY hidden Markov model library has been used to carry out SCOP domain assignments to all genomes at the superfamily level.


Alignments of sequences to 10 models in this superfamily are available by clicking on the 'Alignments' icon above. PDB sequences less than 40% identical are shown by default, but any other sequence(s) may be aligned. Select PDB sequences, genome sequences, or paste in or upload your own sequences.


Browse and view proteins in genomes which have different domain combinations including a Cytochrome b5-like heme/steroid binding domain domain.


Examine the distribution of domain superfamilies, or families, across the major taxonomic kingdoms or genomes within a kingdom. This gives an immediate impression of how superfamilies, or families, are restricted to certain kingdoms of life.


Explore domain occurrence network where nodes represent genomes and edges are domain architectures (shared between genomes) containing the superfamily of interest.

There are 10 hidden Markov models representing the Cytochrome b5-like heme/steroid binding domain superfamily. Information on how the models are built, and plots showing hydrophobicity, match emmission probabilities and insertion/deletion probabilities can be inspected.


Jump to [ Top of page · SCOP classification · InterPro annotation · PDBeMotif links · Functional annotation · Internal database links ]