Peroxisomal ABC transporters: functions and mechanism

Peroxisomes are arguably the most biochemically versatile of all eukaryotic organelles. Their metabolic functions vary between different organisms, between different tissue types of the same organism, and even between different developmental stages or in response to changed environmental conditions. New functions for peroxisomes are still being discovered and their importance is underscored by the severe phenotypes that can arise as a result of peroxisome dysfunction. The β-oxidation pathway is central to peroxisomal metabolism, but the substrates processed are very diverse, reflecting the diversity of peroxisomes across species. Substrates for β-oxidation enter peroxisomes via ATP Binding Cassette (ABC) transporters of the ABCD subfamily and are activated by specific acyl CoA synthetases for further metabolism. Humans have three peroxisomal ABCD family members, which are half transporters that homodimerise and have distinct but partially overlapping substrate specificity; S. cerevisiae has two half transporters that heterodimerise and plants have a single peroxisomal ABC transporter that is a fused heterodimer and which appears to be the single entry point into peroxisomes for a very wide variety of β-oxidation substrates. Our studies suggest that the Arabidopsis peroxisomal ABC transporter AtABCD1 (COMATOSE/PXA1/PED3) accepts acyl CoA substrates, cleaves them before or during transport followed by reactivation by peroxisomal synthetases. We propose that this is a general mechanism to provide specificity to this class of transporters and by which amphipathic compounds are moved across peroxisome membranes

Antagonistic functions of SET-2/SET1 and HPL/HP1 proteins in C. elegans development

AbstractCellular identity during metazoan development is maintained by epigenetic modifications of chromatin structure brought about by the activity of specific proteins which mediate histone variant incorporation, histone modifications, and nucleosome remodeling. HP1 proteins directly influence gene expression by modifying chromatin structure. We previously showed that the Caenorhabditis elegans HP1 proteins HPL-1 and HPL-2 are required for several aspects of post-embryonic development. To gain insight into how HPL proteins influence gene expression in a developmental context, we carried out a candidate RNAi screen to identify suppressors of hpl-1 and hpl-2 phenotypes. We identified SET-2, the homologue of yeast and mammalian SET1, as an antagonist of HPL-1 and HPL-2 activity in growth and somatic gonad development. Yeast Set1 and its mammalian counterparts SET1/MLL are H3 lysine 4 (H3K4) histone methyltransferases associated with gene activation as part of large multisubunit complexes. We show that the nematode counterparts of SET1/MLL complex subunits also antagonize HPL function in post-embryonic development. Genetic analysis is consistent with SET1/MLL complex subunits having both shared and unique functions in development. Furthermore, as observed in other species, we find that SET1/MLL complex homologues differentially affect global H3K4 methylation. Our results suggest that HP1 and a SET1/MLL-related complex may play antagonistic roles in the epigenetic regulation of specific developmental programs

Optimization of odd chain fatty acid production by Yarrowia lipolytica

Background: Odd chain fatty acids (odd FAs) have a wide range of applications in therapeutic and nutritional industries, as well as in chemical industries including biofuel. Yarrowia lipolytica is an oleaginous yeast considered a preferred microorganism for the production of lipid-derived biofuels and chemicals. However, it naturally produces negligible amounts of odd chain fatty acids. Results: The possibility of producing odd FAs using Y. lipolytica was investigated. Y. lipolytica wild-type strain was shown able to grow on weak acids; acetate, lactate, and propionate. Maximal growth rate on propionate reached 0.24 ± 0.01 h−1 at 2 g/L, and growth inhibition occurred at concentration above 10 g/L. Wild-type strain accumulated lipids ranging from 7.39 to 8.14% (w/w DCW) depending on the carbon source composition, and odd FAs represented only 0.01–0.12 g/L. We here proved that the deletion of the PHD1 gene improved odd FAs production, which reached a ratio of 46.82% to total lipids. When this modification was transferred to an obese strain, engineered for improving lipid accumulation, further increase odd FAs production reaching a total of 0.57 g/L was shown. Finally, a fed-batch co-feeding strategy was optimized for further increase odd FAs production, which generated 0.75 g/L, the best production described so far in Y. lipolytica. Conclusions: A Y. lipolytica strain able to accumulate high level of odd chain fatty acids, mainly heptadecenoic acid, has been successfully developed. In addition, a fed-batch co-feeding strategy was optimized to further improve lipid accumulation and odd chain fatty acid content. These lipids enriched in odd chain fatty acid can (1) improve the properties of the biodiesel generated from Y. lipolytica lipids and (2) be used as renewable source of odd chain fatty acid for industrial applications. This work paves the way for further improvements in odd chain fatty acids and fatty acid-derived compound production

Effect of POX genotype and Lip2p overexpression on lactone production and reconsumption by Yarrowia lipolytica using castor oil as substrate

γ-Decalactone production from ricinoleic acid biotransformation by Yarrowia lipolytica has drawn the attention of many authors and, in the last years, molecular and physiological developments were made through the use of engineered strains in novel culture conditions. The purpose of this work was to monitor the performance of modified Y. lipolytica strains in their lipid metabolism specifically at the β-oxidation pathway (MTLY40-2P strain, disrupted in the native genes POX2-5 and expressing an ectopic Aox2p-encoding gene) or at the triglyceride hydrolysis (JMY3010 strain, Lip2p overexpressed) using castor oil as substrate, in a lab-scale bioreactor. Using step-wise fed-batch cultures of MTLY40-2P strain, a γ-decalactone concentration of 7 g L−1 was reached. γ-Decalactone reconsumption was prevented and hydroxylactone production was reduced by Y. lipolytica MTLY40-2P strain. Moreover, substantial increase in the initial rate of aroma production was obtained with strain overexpressing LIP2 gene due to the fast hydrolysis of castor oil.Project ‘BioInd – Biotechnology and Bioengineering for improved Industrial and Agro-Food processes, REF. NORTE-07-0124-FEDER-000028’ co-funded by the Programa Operacional Regional do Norte (ON.2 – O Novo Norte), QREN, FEDER and FCT Strategic Project PEst-OE/EQB/LA0023/2013