Acyl CoA Binding Proteins in Brassica Napus L.: Amino Acid Sequence, Genes and Expression

Abstract

Acyl-CoAs lie at the centre of lipid metabolism in developing seeds since they are the products of fatty acid synthesis by the plastid which are transferred to the ER where they act as substrates for triacylglycerol and phospholipid synthesis [2]. At present it is not clear how the acyl-CoAs are transported within the plant cell and whether the pool of acyl-CoAs resides free in the cytosol or is bound to membranes or proteins. Acyl CoA binding proteins (ACBP) were first reported by [1] as a factor which stimulated fatty acid synthesis in mammary gland extracts. They have been found subsequently in several animals, Drosophila and yeast. ACBPs are cytoplasmic proteins with an Mr of about 10 kDa and they have a very high affinity for binding long chain acyl-CoAs, but they do not bind fatty acids or CoA individually. The concentration of ACBP in some animal systems has been calculated to be higher than that of the acyl-CoA suggesting that the entire cellular pool of acyl-CoA is bound to ACBP. Over expression of the ACBP gene in yeast causes a corresponding increase in acyl-CoA concentration suggesting that the acyl-CoA pool size is influenced by the expression of ACBP genes. Some recent in vitro studies showed that phospholipid and TAG synthesis by microsomes isolated from rat liver are strongly influenced by the ratio of [ACBP] to [acyl-CoA]. When ACBP was in excess, TAG synthesis was strongly reduced but phospholipid synthesis remained unaffected. It is therefore important to determine whether ACBPs are present in plants.