A Natural Variant of the Heme-Binding Signature (R441C) Resulting in Complete Loss of Function of CYP2D6

Abstract

ABSTRACT:A new variant allele CYP2D6*62 (g.4044C>T; R441C) of the drugmetabolizing cytochrome P450 (P450) CYP2D6 was identified in a person with reduced sparteine oxidation phenotype, which was unexpected based on a genetic CYP2D6*1A/*41 background. The recombinantly expressed variant protein had no activity toward propafenone as a result of missing heme incorporation. Sequence alignment revealed that the positively charged R441 residue is part of the heme-binding signature but not strictly conserved among all the P450s. A compilation of described P450 monooxygenase variants revealed that other enzymes can functionally tolerate even nonconservative amino acid changes at the corresponding position (i.e., the invariant cysteine 2). This suggests that heme binding in mammalian P450s depends not only on the integrity of the heme-binding signature but also on other family-and subfamily-specific sequence determinants.

Expression and Functional Analysis of CYP2D6.24, CYP2D6.26, CYP2D6.27, and CYP2D7 Isozymes

“…In contrast, some CYP2D6 alleles including CYP2D6*10 and CYP2D6*17 do produce functional CYP2D6 enzymes, whereas the CYP2D6 allelic isoforms have reduced protein stability and/or drugmetabolizing capacity (Johansson et al, 1994;Yu et al, 2002;Shen et al, 2007). Whereas the enzyme functions of many CYP2D6 allelic variants, including CYP2D6*36, CYP2D6*56, CYP2D6*59, and CYP2D6*62 (Gaedigk et al, 2006;Li et al, 2006;Toscano et al, 2006;Klein et al, 2007), have been determined, the drug-metabolizing capacity of proteins corresponding to other nonsynonymous alleles such as CYP2D6*24 (2853AϾC; I297L), CYP2D6*26 (3277TϾC; I369T), and CYP2D6*27 (3853GϾA; E410K) (supplemental table) that were found in 0.1 to 0.3% of whites (Marez et al, 1997) remain unknown. Understanding the function of individual CYP2D6 alleles will facilitate the translation of genotype information into drug metabolism phenotype (Gaedigk et al, 2008).…”

Polymorphic metabolism by functional alterations of human cytochrome P450 enzymes

“…Allele of CYP2D6*62 was identified in a person with reduced sparteine oxidation phenotype (Klein et al, 2007). This allele contains a variation in the heme-binding signature (R441C), resulting in complete loss of function of CYP2D6 (Klein et al, 2007). A novel SNP of 3318G>A (E383K) associated with CYP2D6*10 was found in Japanese populations and termed as CYP2D6*72 (Matsunaga et al, 2009).…”

“…In this allele, the R344 (CGA) residue in exon 7 was replaced by a stop codon (TGA), resulting in a CYP2D6 enzyme lacking the terminal 153 amino acids, which inactivated the CYP2D6 enzyme activity. Allele of CYP2D6*62 was identified in a person with reduced sparteine oxidation phenotype (Klein et al, 2007). This allele contains a variation in the heme-binding signature (R441C), resulting in complete loss of function of CYP2D6 (Klein et al, 2007).…”

Pharmacogenetic testing revisited: 5&prime;nuclease real-time polymerase chain reaction test panels for genotyping <em>CYP2D6 </em>and <em>CYP2C19</em>

“…These genes primarily code for liver enzymes involved in the metabolization and excretion of a wide range of commonly prescribed drugs. Genetic mutations causing decreased or impaired activity of the mature enzyme have been identified and correlated with increased plasma levels of the substrate and adverse effects in patients 13,17–20. Genetic variations have also been identified causing increased production of an enzyme, and hereby increased metabolism and higher therapeutic levels of prescribed drugs 21,22…”