|Gidda, Satinder -|
|Mullen, Robert -|
Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2012
Publication Date: January 9, 2013
Citation: Pastor, S., Sethumadhavan, K., Ullah, A.H.J., Gidda, S., Cao, H., Mason, C., Chapital, D., Scheffler, B., Mullen, R., Dyer, J., Shockey, J. 2013. Molecular properties of the class III subfamily of acyl-coenyzme A binding proteins from tung tree (Vernicia fordii). Plant Science. 203-204:79-88. Interpretive Summary: Laboratories such as ours that study the processes that oilseeds use to make vegetable oils have found many important genes that contribute to this process. Most of these genes encode enzymes, catalytic proteins that convert one compound into another along the pathway from starting material to end product. However, some important pieces of the puzzle may be other accessory proteins that do not catalyze an actual chemical reaction, but act as “assistants” that carry one component from place to place in the cell. Acyl-CoA binding proteins, or ACBPs, are one such accessory protein. ACBP plays many roles in plant cells, including roles in vegetable oil production. In this study, we have identified four different ACBP proteins that are produced in developing seeds of the tung tree, and have determined many of their fundamental characteristics. Some of these proteins may be useful in our future efforts to use the power of molecular biology to produce valuable novel oils, like tung oil, in traditional domestic oilseed crops.
Technical Abstract: Acyl-CoA binding proteins (ACBPs) have been identified in most branches of life. A single prototypical ACBP was first discovered in yeast, and was found to play a signficant role in lipid metabolism, among other functions. Plants also contain the prototype small, soluble ACBP, but have also evolved various other classes of ACBP genes. The most diverse among these are the class III proteins. Most plants studied to date contain a single class III ACBP gene, however, tung tree (Vernicia fordii) contains two, designated VfACBP3A and VfACBP3B. The two proteins are signficantly different in length and share modest levels of sequence identity, especially in the central regions of the proteins. The gene architecture of both tung ACBP3s reveal signficant evolution in coding and non-coding regions, suggesting either relatively ancient divergence of the two genes from a common ancestor, or possible convergent evolution from two different ancestral genes. These data, plus phylogenetic comparisons of class III proteins from various plant species, suggests that this group is the most evolutionarily dynamic class of ACBP. Both tung ACBP3 genes are expressed at relatively similar levels during tung seed development and in flowers, but ACBP3A is significantly stronger in leaves. Three-dimensional modeling predictions of both tung ACBP3s and Arabidopsis ACBP3 confirmed the presence of the four-helix bundle acyl-CoA binding (ACB) domain shared among all ACBP classes, but also suggested that the folding of the N-terminal regions of these proteins differs substantially. Acyl-CoA binding assays also revealed different affinities for monounsaturated versus very long chain polyunsaturated acyl-CoAs, indicating that the apparent redundancy of function suggested by the gene expression profiles may not extend to the level of protein structure or function. Both proteins, along with ACBP3 from Arabidopsis thaliana, were also transiently expressed in plant cells and their subcellular targeting determined. Our results partially contradict earlier studies, and suggest that at least some class III ACBPs may be predominantly targeted to endoplasmic reticulum membranes, with little or no targeting to the apoplast.