Molecular cloning of the flavin-containing monooxygenase (form II) cDNA from adult human liver.

102

ABSTRACT:The human flavin-containing monooxygenase (form 3) (FMO3) participates in the oxygenation of nucleophilic heteroatom-containing drugs, xenobiotics, and endogenous materials. Currently, six forms of the FMO gene are known, but it is FMO3 that is the major form in adult human liver that is likely responsible for the majority of FMO-mediated metabolism. The substrate structural feature requirements for human FMO3 is beginning to become known to a greater extent and a few chemicals extensively metabolized by FMO3 have been reported. Expression of FMO3 is species-and tissue-specific, but unlike human cytochrome P450, mammalian FMO3 does not appear to be inducible. Interindividual variation in FMO3-dependent metabolism of drugs, chemicals, and endogenous material is therefore more likely due to genetic effects and not environmental ones. Examples of such interindividual variation come from the study of very rare mutations of the human The flavin-containing monooxygenases (FMOs 1 ) (E.C.1.14.13.8) constitute a family of FAD-, NADPH-, and O 2 -dependent microsomal enzymes that catalyze the oxygenation of many nitrogen-, sulfur-, phosphorous-, selenium-, and other nucleophilic heteroatom-containing chemicals (Ziegler, 1980), drugs (Cashman, 1995), and agrichemicals (Hajjar and Hodgson, 1982). There are as many as six forms of mammalian FMO, and some can be present in multiple tissues of the same organism. Some of this information has been previously summarized (Cashman, 2002a). In humans, there is considerable interindividual and interethnic variability in the levels of FMO. In the past few years, a considerable increase in our understanding of the genetic variability of human FMO has occurred and a summary of the current picture focusing on FMO3 will be presented.Evidence for five functional forms of human FMO exist, each encoded by its own gene, that exhibit between 50 to 58% amino acid identity across species lines (Lawton et al., 1994). With the deposit of FMO6 into GenBank, an analysis of the protein encoded by this gene revealed that this protein shares 70% amino acid sequence identity with human FMO3, however, no function for this gene has been described. The description of multiple forms of FMO was advanced by elucidation of the primary sequences by amino acid (Ozols, 1990;Korsmeyer et al., 1998) and nucleotide analysis Lawton et al., 1994;Phillips et al., 1995). As human FMOs were discovered, the common names assigned to enzymes were formalized and a nomenclature was adopted Lawton et al., 1994). The nomenclature was developed on the basis of nucleotide sequence identity. If a human FMO gene has a sequence with Ն82% identity, it is grouped within a family, and the family is indicated by the first numeral of the designation (i.e., 1, 2, 3. . .). The order of naming followed the chronology of publication of the sequence for each member of the family (Dolphin et al., 1997b). The italicized prefix "FMO" is used to designate the gene or an allelic variant. Allelic variants have been observed for FMO that usu...

Section: Hepatic Human Fmomentioning

confidence: 99%

Interindividual Differences of Human Flavin-Containing Monooxygenase 3: Genetic Polymorphisms and Functional Variation

Cashman¹,

Zhang²

2002

102

“…Liver FMO3 is the major human adult isoform and thought to be responsible for most of the FMO-mediated xenobiotic metabolism in the liver (Lomri et al, 1992;Phillips et al, 1995). Expression of FMO3 occurs postpartum.…”

Section: Furnes Et Almentioning

confidence: 99%

Identification of Novel Variants of the Flavin-Containing Monooxygenase Gene Family in African Americans

Furnes¹,

Feng²,

Sommer³

et al. 2003

ABSTRACT:Sequence polymorphisms in enzymes involved in drug metabolism have been widely implicated in the differences observed in the sensitivity to various xenobiotics. The flavin-containing monooxygenase (FMO) gene family in humans catalyzes the monooxygenation of numerous N-, P-and S-containing drugs, pesticides, and environmental toxicants. Six genes (FMO1-6) have been identified so far, but the major alleles of FMO2 and FMO6 encode nonfunctional proteins due to a nonsense mutation and splice-site abnormalities, respectively. Data on structural variants exist for human FMO2 and 3, whereas very little is known about the other FMO genes. FMO1-6 were scanned in 50 individuals of African-American descent using the method, detection of virtually all mutationssingle-strand conformational polymorphism. A total of 49 sequence variants were identified in a total 1.35 megabases of scanned sequence, of which 29 were variants affecting protein structure or expression. Some of these are expected to affect the activity of the protein, including a nonsense mutation in FMO1 (R502X) and missense mutations in FMO1 (I303T), FMO4 (E339Q), and FMO5 (P457L) that occur in highly conserved amino acids. Additional deleterious substitutions in FMO2 (del337G) and FMO6 (Q105X) were also identified. Multiple structural variants in the FMO gene family were observed in this African-American sample. Some of the substitutions identified in this study might be useful markers in future association studies assessing sensitivity to environmental toxicants and common disease.

“…FMO3 is considered a prominent form expressed in adult human liver (Lomri et al, 1992) and plays a role in processing nucleophilic drugs such as the anticancer drug tamoxifen, the pain medication codeine, the antifungal drug ketoconazole, the addictive chemical nicotine found in tobacco, and the diet-derived chemical trimethylamine (Cashman et al, 2000;Ziegler, 2002).…”

Section: Introductionmentioning

confidence: 99%

Effect of Genetic Variants of the Human Flavin-Containing Monooxygenase 3 on N- and S-Oxygenation Activities

Shimizu

Yano²,

Nagashima³

et al. 2006

ABSTRACT:The decreased capacity of the flavin-containing monooxygenase 3 (FMO3) to oxygenate xenobiotics including trimethylamine is believed to contribute to metabolic disorders. The aim of this study was to functionally characterize FMO3 variants recently found in a Japanese population and compare them with selective functional activity of other FMO3 variants. Recombinant Glu158Lys and Glu158Lys-Glu308Gly FMO3 expressed in Escherichia coli membranes showed slightly decreased N-oxygenation of benzydamine and trimethylamine. Selective functional S-oxygenation of these variants by methyl p-tolyl sulfide or sulindac sulfide was comparable to that of wild-type FMO3. The Glu158Lys-Thr201Lys-Glu308Gly and Val257Met-Met260Val variants showed significantly decreased oxygenation of typical FMO3 substrates (i.e., approximately one-tenth of the V max /K m values). Val257Met FMO3 had a lower catalytic efficiency for methyl p-tolyl sulfide and sulindac sulfide S-oxygenation. However, compared with wild-type FMO3, Val257Met FMO3 showed a similar catalytic efficiency for N-oxygenation of benzydamine and trimethylamine. The catalytic efficiency for benzydamine and trimethylamine N-oxygenation by Arg205Cys FMO3 was only moderately decreased, but it possessed decreased sulindac sulfide S-oxygenation activity. Kinetic analysis showed that Arg205Cys FMO3 was inhibited by sulindac in a substrate-dependent manner, presumably because of selective interaction between the variant enzyme and the substrate. The results suggest that the effects of genetic variation of human FMO3 could operate at the functional level for N-and S-oxygenation for typical FMO3 substrates. Genetic polymorphism in the human FMO3 gene might lead to unexpected changes of catalytic efficiency for N-and S-oxygenation of xenobiotics and endogenous materials.The flavin-containing monooxygenase (FMO; EC 1.14.13.8) is an NADPH-dependent enzyme that catalyzes the oxygenation of a wide variety of compounds containing nitrogen, sulfur, or other heteroatoms (Krueger and Williams, 2005;Cashman and Zhang, 2006). FMO3 is considered a prominent form expressed in adult human liver (Lomri et al., 1992) and plays a role in processing nucleophilic drugs such as the anticancer drug tamoxifen, the pain medication codeine, the antifungal drug ketoconazole, the addictive chemical nicotine found in tobacco, and the diet-derived chemical trimethylamine (Cashman et al., 2000;Ziegler, 2002).Because of its strong linkage with the genetic disorder trimethylaminuria, or fish-like odor syndrome, considerable work has been done to relate coding region polymorphisms of the FMO3 gene to interindividual differences in FMO3 phenotype (Dolphin et al., 1997a;Cashman, 2002Cashman, , 2004. According to the list of FMO3 gene mutations summarized in a systematic and trivial name web database, Glu158Lys, Val257Met, and Glu158Lys-Glu308Gly FMO3 forms are common genetic FMO3 polymorphisms (Hernandez et al., 2003). There is considerable genetic variation reported among different ethnic groups (Cashman et al...