3 research outputs found
Design and Mechanism of Tetrahydrothiophene-Based γ‑Aminobutyric Acid Aminotransferase Inactivators
Low levels of γ-aminobutyric
acid (GABA), one of two major
neurotransmitters that regulate brain neuronal activity, are associated
with many neurological disorders, such as epilepsy, Parkinson’s
disease, Alzheimer’s disease, Huntington’s disease,
and cocaine addiction. One of the main methods to raise the GABA level
in human brain is to use small molecules that cross the blood–brain
barrier and inhibit the activity of γ-aminobutyric acid aminotransferase
(GABA-AT), the enzyme that degrades GABA. We have designed a series
of conformationally restricted tetrahydrothiophene-based GABA analogues
with a properly positioned leaving group that could facilitate a ring-opening
mechanism, leading to inactivation of GABA-AT. One compound in the
series is 8 times more efficient an inactivator of GABA-AT than vigabatrin,
the only FDA-approved inactivator of GABA-AT. Our mechanistic studies
show that the compound inactivates GABA-AT by a new mechanism. The
metabolite resulting from inactivation does not covalently bind to
amino acid residues of GABA-AT but stays in the active site via H-bonding
interactions with Arg-192, a π–π interaction with
Phe-189, and a weak nonbonded S···OC interaction
with Glu-270, thereby inactivating the enzyme
Design and Mechanism of Tetrahydrothiophene-Based γ‑Aminobutyric Acid Aminotransferase Inactivators
Low levels of γ-aminobutyric
acid (GABA), one of two major
neurotransmitters that regulate brain neuronal activity, are associated
with many neurological disorders, such as epilepsy, Parkinson’s
disease, Alzheimer’s disease, Huntington’s disease,
and cocaine addiction. One of the main methods to raise the GABA level
in human brain is to use small molecules that cross the blood–brain
barrier and inhibit the activity of γ-aminobutyric acid aminotransferase
(GABA-AT), the enzyme that degrades GABA. We have designed a series
of conformationally restricted tetrahydrothiophene-based GABA analogues
with a properly positioned leaving group that could facilitate a ring-opening
mechanism, leading to inactivation of GABA-AT. One compound in the
series is 8 times more efficient an inactivator of GABA-AT than vigabatrin,
the only FDA-approved inactivator of GABA-AT. Our mechanistic studies
show that the compound inactivates GABA-AT by a new mechanism. The
metabolite resulting from inactivation does not covalently bind to
amino acid residues of GABA-AT but stays in the active site via H-bonding
interactions with Arg-192, a π–π interaction with
Phe-189, and a weak nonbonded S···OC interaction
with Glu-270, thereby inactivating the enzyme
Mechanism of Inactivation of GABA Aminotransferase by (<i>E</i>)- and (<i>Z</i>)‑(1<i>S</i>,3<i>S</i>)‑3-Amino-4-fluoromethylenyl-1-cyclopentanoic Acid
When
γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter
in the mammalian central nervous system, falls below a threshold level,
seizures occur. One approach to raise GABA concentrations is to inhibit
GABA aminotransferase (GABA-AT), a pyridoxal 5′-phosphate-dependent
enzyme that degrades GABA. We have previously developed (1<i>S</i>,3<i>S</i>)-3-amino-4-difluoromethylene-1-cyclopentanoic
acid (CPP-115), which is 186 times more efficient in inactivating
GABA-AT than vigabatrin, the only FDA-approved inactivator of GABA-AT.
We also developed (<i>E</i>)- and (<i>Z</i>)-(1<i>S</i>,3<i>S</i>)-3-amino-4-fluoromethylenyl-1-cyclopentanoic
acid (<b>1</b> and <b>2</b>, respectively), monofluorinated
analogs of CPP-115, which are comparable to vigabatrin in inactivating
GABA-AT. Here, we report the mechanism of inactivation of GABA-AT
by <b>1</b> and <b>2</b>. Both produce a metabolite that
induces disruption of the Glu270–Arg445 salt bridge to accommodate
interaction between the metabolite formyl group and Arg445. This is
the second time that Arg445 has interacted with a ligand and is involved
in GABA-AT inactivation, thereby confirming the importance of Arg445
in future inactivator design