4.4.1.17: Holocytochrome-c synthase
This is an abbreviated version!
For detailed information about Holocytochrome-c synthase, go to the full flat file.
Word Map on EC 4.4.1.17
Reaction
Synonyms
CCHL, ccsA1, cyc2p, CYC3, cytochrome c heme lyase, Cytochrome c heme-lyase, Cytochrome c synthase, HCC synthase, HCCH, HCCS, heme lyase, holocytochrome c synthase, Holocytochrome c synthetase, Holocytochrome c-type synthase, Holocytochrome-C synthase, Holocytochrome-C-type synthase, Synthetase, holocytochrome c, System III
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General Information on EC 4.4.1.17 - Holocytochrome-c synthase
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GENERAL INFORMATION 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
evolution
at least five heme c maturation systems have been identified: Systems I, II, III, IV, and V. System I, the cytochrome c maturation (CCM) system, involves genes ccmA-H5 and is found in various bacteria and in plant mitochondria. System I matures cytochromes c in the periplasmic space of bacteria. System II, cytochrome c synthesis (CCS), consists of four modular components and occurs in various bacteria as well as the thylakoid membranes of plants and algae. System III, also called cytochrome c heme lyase (CCHL), is a single enzyme found in the mitochondria of fungi, vertebrates and invertebrates
metabolism
the enzyme is the primary component of the eukaryotic cytochrome c biogenesis pathway, known as System III
physiological function
additional information
physiological function
C-type cytochromes are distinguished by the covalent attachment of a heme cofactor, a modification that is typically required for its subsequent folding, stability, and function. Heme attachment takes place in the mitochondrial intermembrane space and, in most eukaryotes, is mediated by holocytochrome c synthase
physiological function
cytochrome c, an essential electron carrier in mitochondria and a critical component of the apoptotic pathway, contains a heme cofactor covalently attached to the protein at a conserved CXXCH motif requiring the mitochondrial protein holocytochrome c synthase
physiological function
for mitochondrial cytochrome c assembly, the enzyme binds heme and apocytochrome c substrate to catalyze a covalent attachment of heme by thioether bonds between heme vinyl groups and a conserved CXXCH motif of cytochrome c/c1, and subsequently releases holocytochrome c for proper folding to its native structure, mechanism of assembly, overview
physiological function
human cyts c with deletion of a single residues in helix-1, DELTA M13 cyt c, is poorly matured by human HCCS. Although an HCCS-wild-type cytochrome c complex contains two covalent links, HCCS DELTA M13 cytochrome c contains only one thioether attachment. This attachment is to the second thiol of residues C15SQC18H. The serine residue (of CSQCH) would be anchored where the first cysteine should be in DELTA M13 cytochrome c. An engineered cytochrome c with a CQCH motif in the DELTA M13 background is matured at 2-3fold higher levels
additional information
construction endogenous holocytochrome c mutant variant with a CX3CH motif. The second X residue in the heme binding motif of cyt c1 (CXXCH) is important for its recognition as a substrate by the enzyme
additional information
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the CP motifs, commonly found in heme-binding proteins, are not required for enzyme activity of te Saccharomyyces cerevisiae enzyme, while mutations in the human enzyme on the C-terminal side of the CP motifs cause disease states of microphthalmia with linear skin defects due to abolished or drastically attenuated holocytochrome c production
