The Conversion of Long Chain Saturated Fatty Acids to Their α,β-Unsaturated, β,γ-Unsaturated, and β-Hydroxy Derivatives by Enzymes from the Cellular Slime Mold, Dictyostelium discoideum

Crystal structure of human brain-type fatty acid-binding protein FABP7 complexed with palmitic acid

The brain-type fatty acid-binding protein FABP7, which is expressed in astrocytes and neural progenitors, is a member of the intracellular lipid-binding protein family. This protein is not only involved in various cellular functions such as metabolism, inflammation and energy homeostasis, but also in diseases such as cognitive disorders and tumors. Structures of unsaturated fatty acids, such as oleic acid (OA) and docosahexaenoic acid (DHA), bound to FABP7 have been elucidated; however, structures of saturated fatty acids bound to FABP7 remain unknown. To better understand fatty acid recognition, here the crystal structure of human brain-type fatty acid-binding protein FABP7 complexed with palmitic acid (PA), a saturated fatty acid, is reported at a resolution of 1.6 Å. The PA bound to the fatty acid-binding pocket of FABP7 assumed a U-shaped conformation. The carboxylate moiety of PA interacted with Tyr129, Arg127 and, via a water bridge, with Arg107 and Thr54, whereas its aliphatic chain was stabilized by hydrophobic interactions with Met21, Leu24, Thr30, Thr37, Pro39, Phe58 and Asp77. Structural comparison showed that PA, OA and DHA exhibited unique binding conformations in the fatty acid-binding pocket, stabilized by distinct amino-acid interactions. The binding of PA to FABP7 exhibits a unique binding conformation when compared with other human FABPs (FABP3-FABP5 and FABP8) expressed in other tissues. Based on the crystal and fatty acid structures, it was suggested that PA, which prefers a linear form in nature, required a greater conformational change in its aliphatic chain to bind to the fatty acid-binding pocket in a U-shaped conformation, compared with the cis configurations of OA or DHA. This, together with the length of the aliphatic chain, was considered to be one of the factors determining the binding affinity of PA to FABP7. These results provide a better understanding of fatty acid recognition by FABP7 and expand the knowledge of the binding of PA to FABPs.

Secondary metabolites of slime molds (myxomycetes)

The compounds reported from the slime molds (myxomycetes) species are described. Almost 100 natural compounds including their chemical structures and biological activities are described in this review article. Only metabolites with a well-defined structure are included.

Degradation of unsaturated fatty acids. Identification of intermediates in the degradation of cis-4-decenoly-CoA by extracts of beef-liver mitochondria

1. cis-4-Decenoyl-CoA, an intermediate of linoleic acid catabolism, is degraded by a soluble enzyme fraction of beef liver mitochondria to octanoyl-CoA. cis-2-Octanoly-CoA is not observed among the intermediates of this degradation sequence. 2. The existence of a mitochondrial 4-enoyl-CoA reductase which is distinct from the 2-enoyl-CoA reductase is demonstrated in beef liver. 3. Substrates for the 4-enoyl-CoA reductase are acyl-CoA esters, which possess a 2,4-diene structure rather than those containing an isolated double bond in position 4. 4. The 4-enoyl-CoA reductase is involved in the catabolism of cis-4-decenoyl-CoA. 5. A reaction sequence for the degradation of cis-4-decenoyl-CoA to octanoyl-CoA is proposed which combines the 4-enoyl-CoA reductase with the 'classical' beta-oxidation enzymes.

Synthesis oftrans-3-hexadecenoic acid and oftrans-3-hexadecenoic-1-C14 acid

Thetrans-3-hexadecenoic acid has been synthesized. Physical properties and chemical degradation prove its identity with the acid earlier isolated from several plant lipids. In the sequence of the synthesis, the introduction of a terminal triple bond into commercially available 1-tetradecene was performed by bromination and debromination with KOH and NaNH(2). Chain elongation by a Grignard reaction with CO(2) gave a carboxylic acid with a triple bond in the 2-position. Reduction with LiAlH(4) yielded the corresponding alcohol, and reduction of the triple to thetrans double bond was accomplished with Na in ethanol. Bromination of the alcohol with PBr(3) and conversion of the bromide to the nitrile with KCN or KC(14)N elongated the carbon chain to the desired length. Methanolysis with HCl in methanol and saponification with KOH formed the acid with acceptable yields, and in the case of the C(14)-labeled carboxyl, group, with high specific activity.