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Tuberculosis emerged from its grave to be one of the deadliest diseases of the present time after recently developing a synergy with AIDS. A fatty acid condensing enzyme-mtFabH has been proposed to connect the key processes involved in biosynthesis of mycolic acids, an important component of mycobacterial cell wall. It condenses long acyl Coenzymes A (CoA; up to C20CoA) with malonyl Acyl Carrier Protein (ACP) to form the elongated β-ketoacyl-ACP which further undergoes rounds of elongation to form mero-mycolate branch of mature mycolic acids. Owing to its proposed central position in mycolic acid synthesis, mtFabH has attracted considerable attention as a good anti-mycobacterial target.In this study, we utilized important biochemical tools such as site directed mutagenesis, mass spectrometry and X-ray crystallography to address some of the key unanswered questions regarding the intricate workings of mtFabH. We solved the first co-crystal structure of substrate C12CoA with mtFabH and further analyzed the substrate specificity of this acylation step. This structure depicts the mode of acyl-CoA binding in mtFabH channels; and its comparison with the parallel E.Coli-acetyl CoA structure provides important similarities and differences in substrate binding in these two FabH enzymes. It also posed an important question about the trajectory of long acyl chain CoA into the deep and "seemingly closed" substrate binding pocket of mtFabH. By utilizing disulfide-based inhibitors, we showed that large conformational changes are necessary to facilitate ligand trafficking in mtFabH while the high catalytic turnover rate of the enzyme is maintained. We also proposed the most likely location of the involved loop.A much faster and less cumbersome assay for mtFabH was also developed and it was utilized to characterize a series of inhibitors. This assay utilizes the commercially available radioactive malonyl-CoA in lieu of malonyl-ACP, the physiological substrate, and thus can serve as ACP independent assay for mtFabH.These studies further our understanding of the biochemistry of mtFabH, which along with the faster assay could be helpful in designing potent mtFabH inhibitors as anti-tubercular agents in the future.

Transcriptome analysis based on deep expressed sequence tag (EST) sequencing allows quantitative comparisons of gene expression across multiple species. Using pyrosequencing, we generated over 7 million ESTs from four stages of developing seeds of Ricinus communis, Brassica napus, Euonymus alatus and Tropaeolum majus, which differ in their storage tissue for oil, their ability to photosynthesize and in the structure and content of their triacylglycerols (TAG). The larger number of ESTs in these 16 datasets provided reliable estimates of the expression of acyltransferases and other enzymes expressed at low levels. Analysis of EST levels from these oilseeds revealed both conserved and distinct species-specific expression patterns for genes involved in the synthesis of glycerolipids and their precursors. Independent of the species and tissue type, ESTs for core fatty acid synthesis enzymes maintained a conserved stoichiometry and a strong correlation in temporal profiles throughout seed development. However, ESTs associated with non-plastid enzymes of oil biosynthesis displayed dissimilar temporal patterns indicative of different regulation. The EST levels for several genes potentially involved in accumulation of unusual TAG structures were distinct. Comparison of expression of members from multi-gene families allowed the identification of specific isoforms with conserved function in oil biosynthesis. In all four oilseeds, ESTs for Rubisco were present, suggesting its possible role in carbon metabolism, irrespective of light availability. Together, these data provide a resource for use in comparative and functional genomics of diverse oilseeds. Expression data for more than 350 genes encoding enzymes and proteins involved in lipid metabolism are available at the 'ARALIP' website ().

In many higher plants, seed oil accumulation is governed by complex multilevel regulatory networks including transcriptional regulation, which primarily affects fatty acid biosynthesis. Tree peony (), a perennial deciduous shrub endemic to China is notable for its seed oil that is abundant in unsaturated fatty acids. We discovered that a tree peony trihelix transcription factor, PrASIL1, localized in the nucleus, is expressed predominantly in developing seeds during maturation. Ectopic overexpression of in leaf tissue and seeds significantly reduced total fatty acids and altered the fatty acid composition. These changes were in turn associated with the decreased expression of multitudinous genes involved in plastidial fatty acid synthesis and oil accumulation. Thus, we inferred that PrASIL1 is a critical transcription factor that represses oil accumulation by down-regulating numerous key genes during seed oil biosynthesis. In contrary, up-regulation of oil biosynthesis genes and a significant increase in total lipids and several major fatty acids were observed in silenced tree peony leaves. Together, these results provide insights into the role of trihelix transcription factor PrASIL1 in controlling seed oil accumulation. can be targeted potentially for oil enhancement in tree peony and other crops through gene manipulation.