Disease relevance of CYB5R4

• A genetic approach, using BLAST searches against DBEST for FAD-, NAD(P)H-binding sequences followed by reverse transcription-PCR, was used to clone the complete cDNA sequence of human b5+b5R from the hepatoma cell line Hep 3B [1].
• Variation in NCB5OR: studies of relationships to type 2 diabetes, maturity-onset diabetes of the young, and gestational diabetes mellitus [2].

High impact information on CYB5R4

• NCB5OR appears to play a critical role in protecting pancreatic beta cells against oxidant stress [3].
• We have identified a cytosolic cytochrome b-type NAD(P)H oxidoreductase in mammals, a flavohemoprotein (b5+b5R) containing cytochrome b5 (b5) and b5 reductase (b5R) domains [1].
• Compared with the classical single-domain b5 and b5R proteins localized on endoplasmic reticulum membrane, b5+b5R also has binding motifs for heme, FAD, and NAD(P)H prosthetic groups but no membrane anchor [1].
• The human b5+b5R transcript was expressed at similar levels in all tissues and cell lines that were tested [1].
• When human b5+b5R was expressed as c-myc adduct in COS-7 cells, confocal microscopy revealed a cytosolic localization at the perinuclear space [1].

Biological context of CYB5R4

• Furthermore, genome-wide scans have reported linkage to the chromosome 6q14.2 region close to the human NCB5OR [2].
• The subcellular localization and redox properties of NCB5OR provide important insights into the biology of NCB5OR and the phenotype of the Ncb5or-null mouse [4].

Anatomical context of CYB5R4

• By performing fractionation of subcellular organelles and confocal microscopy, we show that NCB5OR colocalizes with calreticulin, a marker for endoplasmic reticulum [4].

Associations of CYB5R4 with chemical compounds

• We confirm that endogenous NCB5OR indeed has additional NH2-terminal residues [4].
• Recombinant NCB5OR is soluble and has stoichiometric amounts of heme and flavin adenine dinucleotide [4].
• We initially reported human NCB5OR to be a 487-residue soluble protein that reduces cytochrome c, methemoglobin, ferricyanide, and molecular oxygen in vitro [4].

Other interactions of CYB5R4

• The recombinant b5+b5R protein can be reduced by NAD(P)H, generating spectrum typical of reduced cytochrome b with alpha, beta, and Soret peaks at 557, 527, and 425 nm, respectively [1].
• NCB5OR is the first example of an animal flavohemoprotein containing cytochrome b5 and chrome b5 reductase cytodomains [4].
• Kinetic measurements showed that full-length and truncated NCB5OR reduce cytochrome c actively in vitro [4].

Analytical, diagnostic and therapeutic context of CYB5R4

• The redox potential at the heme center of NCB5OR is -108 mV, as determined by potentiometric titrations [4].
• Resonance Raman spectroscopy of NCB5OR presents typical signatures of a six-coordinate low-spin heme similar to those found in other cytochrome b5 proteins [4].
• We therefore considered NCB5OR to be a biological and positional candidate gene and examined the coding region of NCB5OR in 120 type 2 diabetic patients and 63 patients with maturity-onset diabetes of the young using denaturing high-performance liquid chromatography [2].

References