Studies of acyl-CoA dehydrogenase catalyzed allylic isomerization

A one-base or two-base mechanism?

Srikanth Dakoji, Injae Shin, Donald F. Becker, Marian T. Stankovich, Hung Wen Liu

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Acyl-CoA dehydrogenases are flavoproteins that catalyze the conversion of a fatty acyl thioester substrate to the corresponding α,β-enoyl-CoA product. It has been well established that a glutamate residue in the active site [e.g., E367 in short-chain acyl-CoA dehydrogenase (SCAD) of Megasphaera elsdenii] is responsible for the initial α-proton abstraction. Early studies have also shown that this class of enzymes is capable of catalyzing γ-H abstraction to afford the allylic isomerization between α,β- and β,γ-enone thioesters and/or inactivation by 2- or 3-acetylenic acyl-CoA derivatives. Although a dual role has been proposed for the glutamate residue in both α- and γ-deprotonation, the existence of a second active-site basic group to mediate the observed reactions occurring at γ-C remains a feasible mechanism. In an attempt to discern between these two possibilities, we have prepared a few oxirane-containing acyl-CoA derivatives aimed at trapping active-site bases in the vicinity of the α- and/or γ-C. It was found that 2,3-epoxybutyryl-CoA is a new class-selective irreversible inactivator against SCAD; however, the inability of other oxirane-containing probes to react with these enzymes prompted us to tackle this mechanistic problem by directly studying the role of Glu-367 in SCAD-catalyzed 1,3-isomerization. The effect of E367Q mutation on the proficiency of SCAD to mediate the γ-H exchange of crotonoyl-CoA was examined. The capabilities of the wild-type SCAD and its E367Q mutant to catalyze the γ-H abstraction during the inactivation by 2-butynoyl-CoA was also compared. The fact that the mutant protein fails to promote γ-H exchange/abstraction provides strong evidence supporting a one-base mechanism of this enzyme-catalyzed allylic isomerization. Since the catalysis of acyl-CoA dehydrogenases is closely related, such a one-base mechanism is expected to be conserved within this family of enzymes.

Original languageEnglish
Pages (from-to)10971-10979
Number of pages9
JournalJournal of the American Chemical Society
Volume118
Issue number45
DOIs
Publication statusPublished - 1996 Nov 13

Fingerprint

Butyryl-CoA Dehydrogenase
Acyl-CoA Dehydrogenase
Isomerization
Acyl-CoA Dehydrogenases
Coenzyme A
Enzymes
Ethylene Oxide
Catalytic Domain
Acyl Coenzyme A
Glutamic Acid
Derivatives
Flavoproteins
Deprotonation
Mutant Proteins
Catalysis
Protons
Proteins
Mutation
Substrates

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Dakoji, Srikanth ; Shin, Injae ; Becker, Donald F. ; Stankovich, Marian T. ; Liu, Hung Wen. / Studies of acyl-CoA dehydrogenase catalyzed allylic isomerization : A one-base or two-base mechanism?. In: Journal of the American Chemical Society. 1996 ; Vol. 118, No. 45. pp. 10971-10979.
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abstract = "Acyl-CoA dehydrogenases are flavoproteins that catalyze the conversion of a fatty acyl thioester substrate to the corresponding α,β-enoyl-CoA product. It has been well established that a glutamate residue in the active site [e.g., E367 in short-chain acyl-CoA dehydrogenase (SCAD) of Megasphaera elsdenii] is responsible for the initial α-proton abstraction. Early studies have also shown that this class of enzymes is capable of catalyzing γ-H abstraction to afford the allylic isomerization between α,β- and β,γ-enone thioesters and/or inactivation by 2- or 3-acetylenic acyl-CoA derivatives. Although a dual role has been proposed for the glutamate residue in both α- and γ-deprotonation, the existence of a second active-site basic group to mediate the observed reactions occurring at γ-C remains a feasible mechanism. In an attempt to discern between these two possibilities, we have prepared a few oxirane-containing acyl-CoA derivatives aimed at trapping active-site bases in the vicinity of the α- and/or γ-C. It was found that 2,3-epoxybutyryl-CoA is a new class-selective irreversible inactivator against SCAD; however, the inability of other oxirane-containing probes to react with these enzymes prompted us to tackle this mechanistic problem by directly studying the role of Glu-367 in SCAD-catalyzed 1,3-isomerization. The effect of E367Q mutation on the proficiency of SCAD to mediate the γ-H exchange of crotonoyl-CoA was examined. The capabilities of the wild-type SCAD and its E367Q mutant to catalyze the γ-H abstraction during the inactivation by 2-butynoyl-CoA was also compared. The fact that the mutant protein fails to promote γ-H exchange/abstraction provides strong evidence supporting a one-base mechanism of this enzyme-catalyzed allylic isomerization. Since the catalysis of acyl-CoA dehydrogenases is closely related, such a one-base mechanism is expected to be conserved within this family of enzymes.",
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Studies of acyl-CoA dehydrogenase catalyzed allylic isomerization : A one-base or two-base mechanism? / Dakoji, Srikanth; Shin, Injae; Becker, Donald F.; Stankovich, Marian T.; Liu, Hung Wen.

In: Journal of the American Chemical Society, Vol. 118, No. 45, 13.11.1996, p. 10971-10979.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Studies of acyl-CoA dehydrogenase catalyzed allylic isomerization

T2 - A one-base or two-base mechanism?

AU - Dakoji, Srikanth

AU - Shin, Injae

AU - Becker, Donald F.

AU - Stankovich, Marian T.

AU - Liu, Hung Wen

PY - 1996/11/13

Y1 - 1996/11/13

N2 - Acyl-CoA dehydrogenases are flavoproteins that catalyze the conversion of a fatty acyl thioester substrate to the corresponding α,β-enoyl-CoA product. It has been well established that a glutamate residue in the active site [e.g., E367 in short-chain acyl-CoA dehydrogenase (SCAD) of Megasphaera elsdenii] is responsible for the initial α-proton abstraction. Early studies have also shown that this class of enzymes is capable of catalyzing γ-H abstraction to afford the allylic isomerization between α,β- and β,γ-enone thioesters and/or inactivation by 2- or 3-acetylenic acyl-CoA derivatives. Although a dual role has been proposed for the glutamate residue in both α- and γ-deprotonation, the existence of a second active-site basic group to mediate the observed reactions occurring at γ-C remains a feasible mechanism. In an attempt to discern between these two possibilities, we have prepared a few oxirane-containing acyl-CoA derivatives aimed at trapping active-site bases in the vicinity of the α- and/or γ-C. It was found that 2,3-epoxybutyryl-CoA is a new class-selective irreversible inactivator against SCAD; however, the inability of other oxirane-containing probes to react with these enzymes prompted us to tackle this mechanistic problem by directly studying the role of Glu-367 in SCAD-catalyzed 1,3-isomerization. The effect of E367Q mutation on the proficiency of SCAD to mediate the γ-H exchange of crotonoyl-CoA was examined. The capabilities of the wild-type SCAD and its E367Q mutant to catalyze the γ-H abstraction during the inactivation by 2-butynoyl-CoA was also compared. The fact that the mutant protein fails to promote γ-H exchange/abstraction provides strong evidence supporting a one-base mechanism of this enzyme-catalyzed allylic isomerization. Since the catalysis of acyl-CoA dehydrogenases is closely related, such a one-base mechanism is expected to be conserved within this family of enzymes.

AB - Acyl-CoA dehydrogenases are flavoproteins that catalyze the conversion of a fatty acyl thioester substrate to the corresponding α,β-enoyl-CoA product. It has been well established that a glutamate residue in the active site [e.g., E367 in short-chain acyl-CoA dehydrogenase (SCAD) of Megasphaera elsdenii] is responsible for the initial α-proton abstraction. Early studies have also shown that this class of enzymes is capable of catalyzing γ-H abstraction to afford the allylic isomerization between α,β- and β,γ-enone thioesters and/or inactivation by 2- or 3-acetylenic acyl-CoA derivatives. Although a dual role has been proposed for the glutamate residue in both α- and γ-deprotonation, the existence of a second active-site basic group to mediate the observed reactions occurring at γ-C remains a feasible mechanism. In an attempt to discern between these two possibilities, we have prepared a few oxirane-containing acyl-CoA derivatives aimed at trapping active-site bases in the vicinity of the α- and/or γ-C. It was found that 2,3-epoxybutyryl-CoA is a new class-selective irreversible inactivator against SCAD; however, the inability of other oxirane-containing probes to react with these enzymes prompted us to tackle this mechanistic problem by directly studying the role of Glu-367 in SCAD-catalyzed 1,3-isomerization. The effect of E367Q mutation on the proficiency of SCAD to mediate the γ-H exchange of crotonoyl-CoA was examined. The capabilities of the wild-type SCAD and its E367Q mutant to catalyze the γ-H abstraction during the inactivation by 2-butynoyl-CoA was also compared. The fact that the mutant protein fails to promote γ-H exchange/abstraction provides strong evidence supporting a one-base mechanism of this enzyme-catalyzed allylic isomerization. Since the catalysis of acyl-CoA dehydrogenases is closely related, such a one-base mechanism is expected to be conserved within this family of enzymes.

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