Far from Inert: Membrane Lipids Possess Intrinsic Reactivity That Has Consequences for Cell Biology.

In this article, it is hypothesized that a fundamental chemical reactivity exists between some non-lipid constituents of cellular membranes and ester-based lipids, the significance of which is not generally recognized. Many peptides and smaller organic molecules have now been shown to undergo lipidation reactions in model membranes in circumstances where direct reaction with the lipid is the only viable route for acyl transfer. Crucially, drugs like propranolol are lipidated in vivo with product profiles that are comparable to those produced in vitro. Some compounds have also been found to promote lipid hydrolysis. Drugs with high lytic activity in vivo tend to have higher toxicity in vitro. Deacylases and lipases are proposed as key enzymes that protect cells against the effects of intrinsic lipidation. The toxic effects of intrinsic lipidation are hypothesized to include a route by which nucleation can occur during the formation of amyloid fibrils.

Expression, purification and crystallization of acetyl-CoA hydrolase from Neisseria meningitidis.

Neisseria meningitidis is the causative microorganism of many human diseases, including bacterial meningitis; together with Streptococcus pneumoniae, it accounts for approximately 80% of bacterial meningitis infections. The emergence of antibiotic-resistant strains of N. meningitidis has created a strong urgency for the development of new therapeutics, and the high-resolution structural elucidation of enzymes involved in cell metabolism represents a platform for drug development. Acetyl-CoA hydrolase is involved in multiple functions in the bacterial cell, including membrane synthesis, fatty-acid and lipid metabolism, gene regulation and signal transduction. Here, the first recombinant protein expression, purification and crystallization of a hexameric acetyl-CoA hydrolase from N. meningitidis are reported. This protein was crystallized using the hanging-drop vapour-diffusion technique at pH 8.5 and 290 K using ammonium phosphate as a precipitant. Optimized crystals diffracted to 2.0 Šresolution at the Australian Synchrotron and belonged to space group P2(1)3 (unit-cell parameters a = b = c = 152.2 Å), with four molecules in the asymmetric unit.

Re-characterisation of Saccharomyces cerevisiae Ach1p: fungal CoA-transferases are involved in acetic acid detoxification.

Saccharomyces cerevisiae and Neurospora crassa mutants defective in the so-called acetyl-CoA hydrolases Ach1p and Acu-8, respectively, display a severe growth defect on acetate, which is most strongly pronounced under acidic conditions. Acetyl-CoA hydrolysis is an energy wasting process and therefore denoted as a biochemical conundrum. Acetyl-CoA hydrolases show high sequence identity to the CoA-transferase CoaT from Aspergillus nidulans. Therefore, we extensively re-characterised the yeast enzyme. Ach1p showed highest specific activity for the CoASH transfer from succinyl-CoA to acetate and only a minor acetyl-CoA-hydrolase activity. Complementation of an ach1 mutant with the coaT gene reversed the growth defect on acetate confirming the in vivo function of Ach1p as a CoA-transferase. Our results imply that Ach1p is involved in mitochondrial acetate detoxification by a CoASH transfer from succinyl-CoA to acetate. Thereby, Ach1p does not perform the energy wasting hydrolysis of acetyl-CoA but conserves energy by the detoxification of mitochondrial acetate.

Molecular cloning and functional expression of human cytosolic acetyl-CoA hydrolase.

A cDNA encoding human cytosolic acetyl-CoA hydrolase (CACH) was isolated from a human liver cDNA library, sequenced and functionally expressed in insect cells. The human CACH cDNA encodes a 555-amino-acid sequence that is 81.4%/78.7% identical to those of the mouse/rat homologue, suggesting a conserved role for this enzyme in the human and rodent livers. Bioinformatical study further reveals a high degree of similarity among the human and rodent CACHs as follows: First, the gene is composed of 15 exons ranging in size from 56 to 157 bp. Second, the protein consists of two thioesterase regions and a C-terminal steroidogenic acute regulatory protein-related lipid transfer (START) domain. Third, the promoter region is GC-rich and contains GC boxes, but lacks both TATA and CCAAT boxes, the typical criteria of housekeeping genes. A consensus peroxisome proliferator responsive element (PPRE) present in the rodent CACH promoter regions supports marked CACH induction in rat liver by peroxisome proliferator (PP).

Simple and unique purification by size-exclusion chromatography for an oligomeric enzyme, rat liver cytosolic acetyl-coenzyme A hydrolase.

An overview of the purification of an oligomeric enzyme, an extramitochondrial acetyl-coenzyme A hydrolase from rat liver, is presented. The enzyme has been purified to homogeneity using two successive size-exclusion chromatography runs, first for the monomeric and second for the oligomeric form of the enzyme. The sequential gel-filtration steps efficiently removed the contaminants of any molecular size, first of different size from that of the monomeric form of the enzyme (K(av)=0.47 on Superdex 200) and second of different size from that of the oligomeric form (K(av)=0.33), allowing us to purify the enzyme in high purity. This strategy provides an excellent model for purifying many other oligomeric proteins including key enzymes or allosteric enzymes regulating metabolism.

Mouse cytosolic acetyl-CoA hydrolase, a novel candidate for a key enzyme involved in fat metabolism: cDNA cloning, sequencing and functional expression.

A cytosolic acetyl-CoA hydrolase (CACH) cDNA has been isolated from mouse liver cDNA library and sequenced. Recombinant expression of the cDNA in insect cells resulted in overproduction of active acetyl-CoA hydrolyzing enzyme protein. The mouse CACH cDNA encoded a 556-amino-acid sequence that was 93.5% identical to rat CACH, suggesting a conserved role for this enzyme in the mammalian liver. Database searching shows no homology to other known proteins, but reveals homological cDNA sequences showing two single-nucleotide polymorphisms (SNPs) in the CACH coding region. The discovery of mouse CACH cDNA is an important step towards genetic studies on the functional analysis of this enzyme by gene-knockout and transgenic approaches.

Acetyl-CoA hydrolase activity and function in Ascaris suum muscle mitochondria.

Acyl-CoA compounds are stable in adult Ascaris suum mitochondrial preparations. However, when incubated in the presence of 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB), acetyl-CoA or propionyl-CoA are hydrolyzed to form free coenzyme A. This acetyl-CoA hydrolase activity has been partially purified and found to be specific for the above CoA derivatives. Gel filtration indicates an apparent molecular weight of 232,000. The hydrolase activity has been purified free from acyl-CoA transferase activities and appears not to be accounted for on the basis of a thiolase. Because Ascaris is an intestinal parasite that metabolizes primarily anaerobically and accumulates a large number of volatile fatty acids that are formed as the coenzyme A derivatives, the hydrolase would be expected to function in the regeneration of free CoA. However, how the hydrolase reaction would be pulled in the absence of the nonphysiologic DTNB is not known.