Transcriptional and translational mechanisms of cytochrome b5 reductase isoenzyme generation in humans

Abstract

Cytochrome b5 reductase (b5R) is an essential enzyme that exists in soluble and membrane-bound isoforms, each with specific functions. In the rat, the two forms are generated from alternative transcripts differing in the first exons. In contrast, the biogenesis of b5R isoforms in the human is not yet well understood. In the present study we have detected three novel alternative exons, designated 1S, S′ and 1B, located between the first alternative exon 1M and the common second exon in the human b5R gene. Accordingly, multiple M-type, S-type and SS′-type and B-type transcripts are generated. All types of human b5R transcript are expressed ubiquitously. An analysis of in vitro translation products demonstrated an alternative use of different AUG initiators resulting in the production of various human b5R protein isoforms. Our results indicate that the organization of the 5′ region of the b5R gene is not conserved between rodents and humans. Insertion of Alu elements into the human b5R gene, in particular just upstream of the S/S′ region, could be responsible for dynamic events of gene rearrangement during evolution.

NADH Cytochromeb5Reductase and Cytochromeb5Catalyze the Microsomal Reduction of Xenobiotic Hydroxylamines and Amidoximes in Humans

“…NADH cytochrome b 5 reductase is an FAD-containing protein with soluble and membrane-bound forms, each the product of the same gene through alternative promoters and alternative splicing (Tomatsu et al, 1989;Leroux et al, 2001). Both soluble (approximately 32 kDa) and membranebound (approximately 35 kDa) forms of b5R have identical catalytic domains and differ only in a hydrophobic domain at the N terminus of the membrane-bound form.…”

Familial Congenital Methemoglobinemia in Pomeranian Dogs Caused by a Missense Variant in the NADH‐Cytochrome B5 Reductase Gene

“…Genomic DNA was isolated from whole blood with a commercial kit a. It is thought that the membrane‐bound form and soluble form of the enzyme are generated from alternative transcripts differing in the first exon, 1M and 1S, respectively . The canine CYB5R3 gene is located on chromosome 10, and exon 1M is found in the 530 bp gap (chr10: 22820169‐22820698) in the current version of the dog genome (CanFam3.1, NC_006592.3) .…”

“…There are 2 forms of b5R: a membrane‐bound form (the somatic form) and a soluble form (the erythrocytic form), which lacks the membrane anchor domain . Both types of b5R are encoded by the cytochrome b5 reductase ( CYB5R3 ) gene, and in rats and humans, it has reported that they are generated from alternative transcripts differing in the first exon . Two forms are composed of a flavin adenine dinucleotide (FAD) domain and an NADH‐binding domain .…”

Neurological and Neuroimaging Features of CYB5R3-Related Recessive Hereditary Methemoglobinemia Type II

“…The membrane-bound isoform is anchored to the mitochondrial outer membrane, endoplasmic reticulum and plasma membrane of somatic cells and is involved in several metabolic processes including fatty acid desaturation and elongation, cholesterol biosynthesis and cytochrome P450-dependent drug metabolism [ 2 ]. Studies on transcriptional and translational mechanisms of CYB5R3 have clarified that the organization of the 5′ gene region is not conserved between humans and rodents and that insertion of Alu elements into the first exon of the human gene may have contributed to its dynamic evolution [ 3 ]. There are two types of NADH-CYB5R3 deficiency, depending on which isoform is involved.…”