3-hydroxyacyl-ACP dehydratases

Spatially, the enzyme activities are arranged into three different domains. Domain 1 catalyzes the entry of the substrates acetyl CoA and malonyl CoA by [ACPj-S-acetyltransferase [1] and [ACPJ-Smalonyl transferase [2] and subsequent condensation of the two partners by 3-oxoacyl-[ACP] synthase [3]. Domain 2 catalyzes the conversion of the 3-0X0 group to a CH2 group by 3-oxoacyl-[ACP]-reductase [4], 3-hydroxyacyl-[ACP -dehydratase [5], and enoyl-[ACP]-re-... 

Step (3) Dehydration The elements of water are now removed from C-2 and C-3 of D-j3-hydroxybutyryl-ACP to yield a double bond in the product, trans-A2- butenoyl-ACP. The enzyme that catalyzes this dehydration is /3-hydroxyacyl-ACP dehydratase (HD). 

A molecule of water is removed to introduce a double bondl Domain 3-Hydroxyacyl-ACP dehydratase. 

Dehydration of D-3-hydroxybutyryl-ACP to produce crotonyl-ACP (catalyzed by 3-hydroxyacyl-ACP dehydratase). 

Acyl carrier protein (ACP) Acetyi-CoA-ACP transacetyiase (AT) j3-Ketoacyi-ACP synthase (KS) Malonyl-CoA-ACP transferase (MT) /3-Ketoacyl-ACP reductase (KR) /3-Hydroxyacyl-ACP dehydratase (HD) Enoyl-ACP reductase (ER)... 

Fig. 2 Metabolic routes for mcl-PHA biosynthesis. Pseudomonas putida GPol synthesizes PHA through P-oxidation and P. putida KT2440 synthesizes PHA through fatty add de novo synthesis. Special PHA consisting of 4-hydroxyalkanoate, 5- hydroxyalkanoate, or 6-hydroxyalkanoate can be produced by various bacteria when suitable precursors are supplied. 1 acyl-CoA synthetase, 2 acyl-CoA dehydrogenase, 3 enoyl-CoA hydratase, 4 NAD-dependent (5)-3-hydroxyacyl-CoA dehydrogenase, 5 3-ketoacyl-CoA thiolase, 6 (ItFspecific enoyl-CoA hydratase, 7 NADPH-dependent 3-ketoacyl-CoA reducatase, 8 3-hydroxyacyl-CoA epimerase, 9 mcl-PHA polymerase, 10 acetyl-CoA carboxylase, 11 malonyl-CoA-acyl carrier protein (ACP) tiansacylase, 12 3-keto-ACP synthase, 13 3-keto-ACP reductase, 14 3-hydroxyacyl-ACP dehydratase, 15 enoyl-ACP reductase, 16 acyl-ACP thiolase, 17 (l )-3-hydroxyacyl-ACP-CoA transacylase, 18 mcl-PHA polymerase...

Figure 3.2 Enzyme systems associated with the de novo synthesis of fatty acids in the plastid. (a) Acetyl-CoA carboxylase (EC 6.4.1.2) (b) [acyl-carrier protein] (ACP) acetyl-transferase (EC 2.3.1.38) (c) [ACP] malonyltransferase (EC 2.3.1.39) (dl) 3-oxoacyl-[ACP] synthase I (d2) 3-oxoacyl-[ACP] synthase II (EC 2.3.1.41) (d3) 3-oxoacyl-[ACP] synthase III (e) 3-oxoacyl-[ACP] reductase (EC 1.1.1.100) (f) 3-hydroxyacyl-[ACP] dehydratase (g) enoyl-[ACP] reductase (EC 1.3.1.9/10) (d)-(g) constitutes fatty acid synthase...

Hydroxyacyl-ACP dehydratase. The activity of 3-hydroxyacyl-ACP dehydratase has received little attention although a broad specificity (C4-Cie) is recognized to exist for the carbon chain length of the substrate (Shimakata and Stumpf, 1982c). This particular system would not appear to be a good candidate for key regulation or for useful manipulation. 

FIGURE 11.5 Biosynthetic pathway of MCL-PHAs and LCL-PHAs in Pseudomonas aeruginosa using fatty acid synthesis pathway. Enzymes 1 Ketoacyl-ACP synthase, 2 Ketoacyl-ACP reductase, 3 3-Hydroxyacyl-ACP dehydratase, 4 Enoyl-ACP reductase, 5 3-Hydroxyacyl-ACP-CoA transacylase and 6 PHA polymerase (Tiimn and Steinbuchel, 1990 Steinbuchel, 1996 Singh and Mallick, 2008 Singh and Mallick, 2009b). 

Figure 22.4 A simplified illustration of saturated fatty acid biosynthesis in microalgal chloroplast. ACCase, Acetyl-CoA carboxylase ACP, acyl carrier protein CoA, coenzyme A ENR, enoyl-ACP reductase HD, 3-hydroxyacyl-ACP dehydratase KAR, 3-ketoacyl-ACP reductase KAS, 3-ketoacyl-ACP synthase MAT, malonyl-CoA ACP transacylase.

The insertion of a single double bond by an oxygen-independent process has recently been shown to be even more intimately associated with fatty acid synthesis, when a 3-cw-dehydratase, acting at the hydroxyacyl-ACP level, was characterized as an inherent activity of an unusual synthetase complex from Brevibacterium ammoniagenes (Kawaguchi and Okuda, 1977). In this case, oleoyl-CoA has been defined as the product, since unsaturation is retained at the C-9 position. 

Abbreviations FASN, fatty acid synthase ACC, acetyl-CoA-carboxylase ACL, ATP-citrate lyase NADPH, nicotinamide adenine dinucleotide phosphate MAT, malonyl acetyl transferases KS, ketoacyl synthase KR, p-ketoacyl reductase DH, p-hydroxyacyl dehydratase ER, enoyl reductase TE, thioesterase ACP, acyl carrier protein VLCFA, very long chain fatty acids ELOVL, elongation of very long chain fatty acids SCDl, stearoyl-CoA desaturase-1 AMPK, AMP-activated kinase ME, malic enzyme FASKOL, liver-specific deletion of FAS PPARa, Peroxisome Proliferator-Activating Receptor alpha HMG-CoA, 3-hydroxy-3-methyl-glutaryl-CoA SREBP, sterol response element binding protein SIP, site-one protease S2P, site-two... 

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