Disease relevance of CYB5

• Cloning and characterization of a yeast cytochrome b5-encoding gene which suppresses ketoconazole hypersensitivity in a NADPH-P-450 reductase-deficient strain [1].
• Expression of the S. cerevisiae FAH1 cytochrome b5 domain in Escherichia coli produces a soluble protein that exhibits the typical oxidized versus reduced differential absorbance spectra of cytochrome b5 [2].

High impact information on CYB5

• The cytochrome domain closely resembles microsomal cytochrome b5, whereas the flavin-binding domain contains a parallel beta 8/alpha 8 barrel motif similar to glycolate oxidase and trimethylamine dehydrogenase [3].
• Dap1p is related to cytochrome b5, which activates cytochrome P450 proteins, elevating the metabolism of lipids and xenobiotic compounds [4].
• The resulting P. patens cDNA encodes a 480-amino acid polypeptide that contains a predicted N-terminal cytochrome b5-like domain as well as three histidine-rich domains [5].
• The b5 core domain shows a 52% identity and 70% similarity to that of the yeast microsomal cytochrome b5 and a 35% identity and 54% similarity to the b5 core domain of OLE1, the S. cerevisiae Delta-9 fatty acid desaturase [2].
• A search of the Saccharomyces cerevisiae genome data base for cytochrome b5-like sequences identified a 1.152-kilobase pair open reading frame, located on chromosome XIII at locus YMR272C (FAH1) [2].

Biological context of CYB5

• Based on this phenotype, the CYB5 gene in the human pathogen Candida albicans was investigated to determine whether the cyb5 genotype was viable and would also demonstrate azole sensitivity [6].
• This alternative catalytic cycle, where both the first and second electrons were donated via the NADH cytochrome b5 electron transport system, can account for the continued ergosterol production seen in yeast strains containing a disruption of the gene encoding CPR [7].
• Biodiversity of the P450 catalytic cycle: yeast cytochrome b5/NADH cytochrome b5 reductase complex efficiently drives the entire sterol 14-demethylation (CYP51) reaction [7].
• Selection for azole resistance following expression of a cDNA library constructed with RNA from progesterone-treated R. nigricans in the yeast Saccharomyces cerevisiae led to the identification of CPR1-FL and CYB5-1 cDNAs, which code for functionally competent NADPH-cytochrome P450 reductase and cytochrome b5, respectively [8].
• Studies of single turnover kinetics with a small molecule (ascorbate) or within bound complexes with either cytochrome b5 or cytochrome c peroxidase demonstrated that redox kinetics are only slightly affected by these substitutions [9].

Anatomical context of CYB5

• Purification and characterization of intact cytochrome b5 from yeast microsomes [10].
• In the presence of low concentrations of Triton X-100, it interacts effectively with the intact form of NADH-cytochrome b5 reductase purified either from yeast microsomes or from rabbit liver microsomes [10].
• Replacement of Ser-104 to Met-125, the putative membrane-anchoring domain of cytochrome b5, with 22 leucine residues results in a protein which targets to the endoplasmic reticulum but the extent of its reduction is only 50% of that of the wild type in yeast microsomes [11].
• In order to accommodate the markedly increased amount of the membrane-bound cytochrome b5, the yeast cell proliferated its nuclear membrane [12].
• A model system for studying membrane biogenesis. Overexpression of cytochrome b5 in yeast results in marked proliferation of the intracellular membrane [12].

Associations of CYB5 with chemical compounds

• Cytochrome b(5) is required for sterol C5-6 desaturation and the encoding gene, CYB5, is nonessential in Saccharomyces cerevisiae [6].
• Substrate-induced spectra revealed that the dissociation constant of the fused enzyme for testosterone significantly decreased with coexpression of human cytochrome b5 [13].
• The involvement of cytochrome b5 in palmitoyl-CoA desaturation by yeast microsomes was studied by using yeast mutants requiring unsaturated fatty acids and an antibody to yeast cytochrome b5 [14].
• The cytochrome b5 content in microsomes from mutant Ole 3 could be varied by changing the delta-aminolevulinic acid concentration in the growth medium, and the desaturase activity of the microsomes increased as their cytochrome b5 content was increased [14].
• Microsomes from mutant Ole 3 grown with Tween 80 plus ergosterol were devoid of both the desaturase activity and cytochrome b5, but those from delta-aminolevulinic acid-grown mutant Ole 3 contained cytochrome b5 and catalyzed the desaturation [14].

Other interactions of CYB5

• Synthesis of monohydroxylated inositolphosphorylceramide (IPC-C) in Saccharomyces cerevisiae requires Scs7p, a protein with both a cytochrome b5-like domain and a hydroxylase/desaturase domain [15].

Analytical, diagnostic and therapeutic context of CYB5

• Site-directed mutagenesis studies of the membrane binding domain of cytochrome b5 provided additional clues about the nature of the signal for membrane proliferation [12].
• A new sequence alignment is proposed for the two proteins, and a few structural considerations are presented, based on the inspection of calf liver cytochrome b5 three-dimensional model [50,51] [16].
• We have successfully designed and used a set of oligonucleotides to synthesize the Saccharomyces cerevisiae cytochrome b5 by using both LCR and assembly PCR [17].

References