Evaluation of the amount of acyl-CoA elongases in leek (Allium porrum L) leaves

The Endoplasmic reticulum-associated maize GL8 protein is a component of the acyl-coenzyme A elongase involved in the production of cuticular waxes

The gl8 gene is required for the normal accumulation of cuticular waxes on maize (Zea mays) seedling leaves. The predicted GL8 protein exhibits significant sequence similarity to a class of enzymes that catalyze the reduction of a ketone group to a hydroxyl group. Polyclonal antibodies raised against the recombinant Escherichia coli-expressed GL8 protein were used to investigate the function of this protein in planta. Subcellular fractionation experiments indicate that the GL8 protein is associated with the endoplasmic reticulum membranes. Furthermore, polyclonal antibodies raised against the partially purified leek (Allium porrum) microsomal acyl-coenzyme A (CoA) elongase can react with the E. coli-expressed GL8 protein. In addition, anti-GL8 immunoglobulin G inhibited the in vitro elongation of stearoyl-CoA by leek and maize microsomal acyl-CoA elongase. In combination, these findings indicate that the GL8 protein is a component of the acyl-CoA elongase. In addition, the finding that anti-GL8 immunoglobulin G did not significantly inhibit the 3-ketoacyl-CoA synthase, 3-ketoacyl-CoA dehydrase, and (E) 2,3-enoyl-CoA reductase partial reactions of leek or maize acyl-CoA elongase lends further support to our previous hypothesis that the GL8 protein functions as a beta-ketoacyl reductase during the elongation of very long-chain fatty acids required for the production of cuticular waxes.

Arginyl residues are involved in acyl-CoA binding to the elongase from etiolated leek seedlings

The C18:0-CoA elongase from etiolated leek seedling microsomes was inactivated by treatment with phenylglyoxal, a reagent which specifically modifies arginyl residues. In the presence of 20 mM phenylglyoxal, 95% of the C18:0-CoA elongation was inhibited. The condensation and dehydration reactions of the overall elongation were totally inhibited, whereas enoyl-CoA reductase activity was diminished by 75%, but the nature of the final elongation product was unchanged. Phenylglyoxal did not modify the C18:0-CoA partition between membrane and aqueous compartments; moreover, [1-14C]phenylglyoxal labeling experiments showed a covalent binding of the inhibitor to membrane proteins. The ability of several substrates to prevent the inactivation by phenylglyoxal was investigated. NADH and NADPH had no effect. CoA led to a 75% protection, and the incorporation of [14C]phenylglyoxal was strongly affected by 10 mM CoA. The acyl chain length of the acyl-CoAs played also a crucial role in preventing the binding of phenylglyoxal. The maximal prevention of phenylglyoxal inhibition was obtained with C18:0-CoA. This suggests that arginyl residues could be present in the vicinity of the acyl-CoA binding site of the subunits of C18:0-CoA elongase.

Antibodies to long-chain acyl-CoAs. A new tool for lipid biochemistry

Antibodies directed against long chain acyl-CoAs (having 16 and 18 carbon atoms) have been prepared and are reported for the first time. A modified ELISA procedure adapted to these amphiphilic molecules has been developed: it is a rapid, simple and sensitive test permitting to detect as little as 3 pmol of acyl-CoA. These antibodies represent a new tool for studying long-chain acyl-CoAs. Their use in an immunochemical approach for the study of protein-acyl-CoA interactions is presented.

Occurrence and sequence of a DnaJ protein in plant (Allium porrum) epidermal cells

Antibodies raised against a purified fraction from microsomal membranes of leek epidermal cells were used to screen a lambda zap expression library from epidermal cells of leak plants. A near full-length clone was isolated. This cDNA contains an open reading-frame of 1,191 bp coding for a DnaJ protein (leek DNAJ 1 or LDJ1). Leek DnaJ1 represents the second protein of this type described in a pluricellular organism, the first being that sequenced from human cells.