The interaction of brain lipids with ␣-synuclein may play an important role in the pathogenesis of Parkinson disease (PD). Docosahexaenoic acid (DHA) is an abundant fatty acid of neuronal membranes, and it is presents at high levels in brain areas with ␣-synuclein inclusions of patients with PD. In animal models, an increase of DHA content in the brain induces ␣-synuclein oligomer formation in vivo. However, it is not clear whether these oligomeric species are the precursors of the larger aggregates found in Lewy bodies of post-mortem PD brains. To characterize these species and to define the role of fatty acids in amyloid formation, we investigated the aggregation process of ␣-synuclein in the presence of DHA. We found that DHA readily promotes ␣-synuclein aggregation and that the morphology of these aggregates is dependent on the ratio between the protein and DHA. In the presence of a molar ratio protein/DHA of 1:10, amyloid-like fibrils are formed. These fibrils are morphologically different from those formed by ␣-synuclein alone and have a less packed structure. At a protein/DHA molar ratio of 1:50, we observe the formation of stable oligomers. Moreover, chemical modifications, methionine oxidations, and proteinlipid adduct formations are induced by increasing concentrations of DHA. The extent of these modifications defines the structure and the stability of aggregates. We also show that ␣-synuclein oligomers are more toxic if generated in the presence of DHA in dopaminergic neuronal cell lines, suggesting that these species might be important in the neurodegenerative process associated with PD.

Polyamine oxidases (PAOs) are flavin-dependent enzymes involved in polyamine catabolism. In Arabidopsis five PAO genes (AtPAO1-AtPAO5) have been identified which present some common characteristics, but also important differences in primary structure, substrate specificity, subcellular localization, and tissue-specific expression pattern, differences which may suggest distinct physiological roles. In the present work, AtPAO5, the only so far uncharacterized AtPAO which is specifically expressed in the vascular system, was partially purified from 35S::AtPAO5-6His Arabidopsis transgenic plants and biochemically characterized. Data presented here allow AtPAO5 to be classified as a spermine dehydrogenase. It is also shown that AtPAO5 oxidizes the polyamines spermine, thermospermine, and N(1)-acetylspermine, the latter being the best in vitro substrate of the recombinant enzyme. AtPAO5 also oxidizes these polyamines in vivo, as was evidenced by analysis of polyamine levels in the 35S::AtPAO5-6His Arabidopsis transgenic plants, as well as in a loss-of-function atpao5 mutant. Furthermore, subcellular localization studies indicate that AtPAO5 is a cytosolic protein undergoing proteasomal control. Positive regulation of AtPAO5 expression by polyamines at the transcriptional and post-transcriptional level is also shown. These data provide new insights into the catalytic properties of the PAO gene family and the complex regulatory network controlling polyamine metabolism.

HighlightA combined untargeted approach was adopted to achieve a picture of the transcriptional and proteomic profiles typifying the maize root transition zone in response to nitrate.

The existence of a gamma-glutamyl cycle consisting of intracellular GSH synthesis, extrusion to the apoplastic space and recovery by gamma-glutamyl transferase (GGT)-assisted degradation into its constituent amino acids, has been demonstrated in plants. To address the significance of this cycle in plant cells, we performed integrated biochemical, immunocytochemical, and quantitative proteomics analyses in the Arabidopsis thaliana ggt1 knockout mutant (lacking apoplastic GGT1 isoform) and its corresponding wild-type (WT). The ggt1 knockout leaves exhibited an increased ascorbate and GSH content, increased apoplastic GSH content, and enhanced protein carbonylations in the low-molecular weight range compared to WT. The combined iTRAQ and LC-MS/MS-based quantitative proteomics approach identified 70 proteins (out of 1013 identified proteins) whose abundance was significantly different in leaves of ggt1 mutant compared to WT, with a fold change ≥1.5. Mining of the proteome data for GSH-associated genes showed that disruption of gamma-glutamyl cycle in ggt1 knockout-leaves was associated with the induction of genes encoding four GSTs in the phi class (GSTF2, GSTF6, GSTF9, and GSTF10), a GSH peroxidase (GPX1), and glyoxylase II. Proteins with a lower abundance compared to the WT are involved in chloroplast functions, carbohydrate/maltose metabolism, and vegetative storage protein synthesis. Present findings suggest that GGT1 plays a role in redox signaling. The disruption of the gamma-glutamyl cycle in the ggt1 mutant results in pleiotropic effects related to biotic and abiotic stress response, antioxidant metabolism, senescence, carbohydrate metabolism, and photosynthesis, with strong implications for plant adaptation to the environment.