Molecular Identification and Characterization of the Arabidopsis Δ3,5,Δ2,4-Dienoyl-Coenzyme A Isomerase, a Peroxisomal Enzyme Participating in the β-Oxidation Cycle of Unsaturated Fatty Acids

Abstract

Degradation of unsaturated fatty acids through the peroxisomal b-oxidation pathway requires the participation of auxiliary enzymes in addition to the enzymes of the core b-oxidation cycle. The auxiliary enzyme D 3,5 ,D 2,4 -dienoyl-coenzyme A (CoA) isomerase has been well studied in yeast (Saccharomyces cerevisiae) and mammals, but no plant homolog had been identified and characterized at the biochemical or molecular level. A candidate gene (At5g43280) was identified in Arabidopsis (Arabidopsis thaliana) encoding a protein showing homology to the rat (Rattus norvegicus) D Catabolism of fatty acids occurs primarily through the b-oxidation cycle. In plants, b-oxidation is located in peroxisomes, while in animal cells, it occurs in both peroxisomes and mitochondria (for review, see Gerhardt, 1992;Graham and Eastmond, 2002;Hooks, 2002). b-Oxidation is of primary importance for seedling establishment following germination since it allows the breakdown of fatty acids stored in triacylglycerides into acetyl-CoA, which is subsequently converted to Glc via the glyoxylate cycle and gluconeogenesis (Hayashi et al., 1998;Germain et al., 2001). Although b-oxidation is very active during germination, this cycle is also present in mature photosynthetic tissues, as well as in developing seeds Graham and Eastmond, 2002).The peroxisomal core b-oxidation cycle in plants is composed of four enzymatic activities located on three proteins. The first enzyme is acyl-CoA oxidase, converting acyl-CoA into 2-trans-enoyl-CoA. The second is a multifunctional enzyme that harbors two activities in a single polypeptide, namely, an enoyl-CoA hydratase and a 3-hydroxyacyl-CoA dehydrogenase, catalyzing the successive conversion of 2-trans-enoyl-CoA into 3-hydroxyacyl-CoA and 3-ketoacyl-CoA, respectively. The final enzyme is the 3-ketothiolase and is responsible for cleavage of 3-ketoacyl-CoA to form acetyl-CoA and an acyl-CoA that is two carbons shorter and that can reenter the b-oxidation spiral. In Arabidopsis (Arabidopsis thaliana), at least four genes have been characterized to encode for acyl-CoA oxidases with different chain-length specificities, two genes encode for multifunctional enzymes, and four genes encode 3-ketothiolases (Graham and Eastmond, 2002).In contrast to the degradation of saturated fatty acids, which can be mediated completely by the four enzymatic activities of the core b-oxidation cycle, the degradation of several types of unsaturated fatty acids has been shown to require the presence of auxiliary enzymes Hiltunen et al., 2003;van Roermund et al., 2003). This is because the core b-oxidation functions through a 2-trans-enoyl-CoA intermediate while many fatty acids have unsaturated bonds either on an odd-numbered carbon or in the Article, publication date, and citation information can be found at www.plantphysiol.org/cgi

Biochemistry of apple aroma: A review

“…β-Oxidation of fatt y acids β-Oxidation is the main pathway involved in the degradation of fatt y acids, and in plants it is mainly performed in peroxisomes (86)(87)(88), which contain all the necessary enzymes. During β-oxidation, fatt y acids are activated to their corresponding acyl coenzyme A (CoA) by acyl-CoA synthase in a reaction requiring adenosine triphosphate (ATP), Mg 2+ and coenzyme A with sulfh ydryl functional group (CoASH) (89,90).…”

“…The products of oxidation and breakdown are acetyl-CoA and propionyl-CoA (91). The enzymes of the main β-oxidation cycle are able to catabolize linear saturated fatt y acids or those with double trans bonds in the ∆ 2 position (86,89,90). Some linear fatt y acids with double cis bonds have odd number of carbon atoms and they form enoyl-CoA molecules that cannot be metabolized by the enzymes of the main β-oxidation cycle.…”

“…-dienoyl-CoA isomerase that catalyzes the conversion of 3,5-dienoyl-CoA to 2,4-dienoyl-CoA (86,87). All these enzymes are required for the conversion of fatt y acids in plants (90).…”

“…Fig. 1 shows the enzymes, cofactors and products involved in the degradation of stearic, oleic and linoleic acids, all present in apples, through the β-oxidation pathway (86,87,(89)(90)(91). The β-oxidation of long-chain fatt y acids produces shorter acids such as acetic, butanoic and hexanoic acids, which can be reduced to their corresponding alcohols (16) before being esterifi ed with acyl-CoA by the alcohol acyltransferase (AAT) enzyme.…”

Función del gen 3-cetoacil-CoA tiolasa 2 (KAT2) en defensa y desarrollo. Participación de los peroxisomas en las respuestas a herida en Arabidopsis thaliana.

“…En Arabidopsis, se ha descrito la participación de las ACS LONG-CHAIN ACYL-COA SYNTHETASE 6 y 7 (LACS 6 y LACS7) (Fulda et al, 2002), dos enzimas con actividad OPC-8:0 CoA Ligasa 1 (OPCL1) Kienow et al, 2008) y otras dos ACS (Schneider et al, 2005) -dienoil-CoA isomerasa y 2,4-dienoil-CoA reductasa, para dar lugar al compuesto 2-trans-enoil-CoA derivado (Kunau et al, 1995;Hiltunen y Qin, 2000). Estas actividades auxiliares, fundamentales en plantas donde la mayoría de los ácidos grasos son poliinsaturados en átomos de carbono pares y/o impares, pueden ser realizadas por la propia MFP Preisig-Muller et al, 1994) o por otras enzimas con dichas actividades individuales (Goepfert et al, 2005;. En el paso final de la β-oxidación, la enzima 3-cetoacil-CoA _______________________________________________________________Introducción tiolasa (KAT) cataliza la rotura del enlace tioester del 3-cetoacil-CoA derivado, liberando acetil-CoA, producto final de la ruta y el correspondiente acil-CoA derivado con dos unidades de carbono menos, que es susceptible de una nueva ronda de β-oxidación.…”