Characterization of Sulfoxygenation and Structural Implications of Human Flavin-Containing Monooxygenase Isoform 2 (FMO2.1) Variants S195L and N413Ks

• Published in: Drug metabolism and disposition Vol. 37; no. 8; pp. 1785 - 1791
• Main Authors: KRUEGER, Sharon K, HENDERSON, Marilyn C, SIDDENS, Lisbeth K, VANDYKE, Jonathan E, BENNINGHOFF, Abby D, KARPLUS, P. Andrew, FURNES, Bjarte, SCHLENK, Daniel, WILLIAMS, David E
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 06-05-2009
• Subjects: Biological and medical sciences; Medical sciences; Pharmacology. Drug treatments; Characterization; Human; Variant; Genotype; Molecular form; Genetic variability
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.109.027201

Catalytically active human flavin-containing monooxygenase isoform 2
(FMO2.1) is encoded by an allele detected only in individuals of African or
Hispanic origin. Genotyping and haplotyping studies indicate that S195L and
N413K occasionally occur secondary to the functional
FMO2*1
allele
encoding reference protein Gln472. Sulfoxygenation under a range of conditions
reveals the role these alterations may play in individuals expressing active
FMO2 and provides insight into FMO structure. Expressed S195L lost rather than
gained activity as pH was increased or when cholate was present. The activity
of S195L was mostly eliminated after heating at 45°C for 5 min in the
absence of NADPH, but activity was preserved if NADPH was present. By
contrast, Gln472 was less sensitive to heat, a response not affected by NADPH.
A major consequence of the S195L mutation was a mean 12-fold increase in
K
m
for NADPH compared with Gln472. Modeling an S213L
substitution, the equivalent site, in the structural model of FMO from the
Methylophaga
bacterium leads to disruption of interactions with
NADP
+
. N413K had the same pattern of activity as Gln472 in response
to pH, cholate, and magnesium, but product formation was always elevated by
comparison. N413K also lost more activity when heated than Gln472; however,
NADPH attenuated this loss. The major effects of N413K were increases in
velocity and
k
cat
compared with Gln472. Although these
allelic variants are expected to occur infrequently as mutations to the
FMO2*1
allele, they contribute to our overall understanding of
mammalian FMO structure and function.