No abstract

These results suggest that AOX1A plays a significant role in sustaining the chloroplastic redox state and energization to optimize photosynthesis by regulating cellular redox homeostasis and ROS generation when electron transport through the COX pathway is disturbed at complex III.

The Chlamydomonas reinhardtii tla1 (truncated light-harvesting chlorophyll antenna size) mutant was generated upon DNA insertional mutagenesis and shown to specifically possess a smaller than wild type (WT) chlorophyll antenna size in both photosystems. Molecular and genetic analysis revealed that the exogenous plasmid DNA was inserted at the end of the 5' UTR and just prior to the ATG start codon of a hitherto unknown nuclear gene (termed Tla1), which encodes a protein of 213 amino acids. The Tla1 gene in the mutant is transcribed with a new 5' UTR sequence, derived from the 3' end of the transforming plasmid. This replacement of the native 5' UTR and promoter regions resulted in enhanced transcription of the tla1 gene in the mutant but inhibition in the translation of the respective tla1 mRNA. Transformation of the tla1 mutant with WT Tla1 genomic DNA successfully rescued the mutant. These results are evidence that polymorphism in the 5' UTR of the Tla1 transcripts resulted in the tla1 phenotype and that expression of the Tla1 gene is a prerequisite for the development/assembly of the Chl antenna in C. reinhardtii. A blast search with the Tla1 deduced amino acid sequence

Increased triglyceride-rich lipoproteins (TGRLs) in the postprandial state are associated with atherosclerosis. We investigated whether the postprandial state induced structural changes at the apolipoprotein E4 (apoE4) C terminus, its principal lipid binding domain, using electron paramagnetic resonance (EPR) spectroscopy of a site-directed spin label attached to the cysteine of apoE4-W264C. Spin coupling between labels located in the C termini was followed after mixing with preprandial and postprandial human plasma samples. Our results indicate that postprandial plasma triggers a reorganization of the protein such that the dipolar broadening is diminished, indicating a reduction in Cterminal interaction. The loss of spectral broadening was directly correlated with an increase in postprandial plasma triglycerides and was reduced with delipidated plasma. The spin-labeled apoE4 displayed a lipid preference of VLDL . LDL . HDL in the preprandial and postprandial states. The apoE4 shift to VLDL during the postprandial state was accompanied by a loss in spectral broadening of the protein. These findings suggest that apoE4 associated with LDL maintains self-association via its C terminus and that this association is diminished in VLDL-associated protein. Lipolyzed TGRL reflected a depletion of the C-terminal interaction of apoE4. Addition of palmitate to VLDL gave a similar response as lipolyzed TGRL, suggesting that lipolysis products play a major role in reorganizing apoE4 during the postprandial state. Apolipoprotein E (apoE) is a 34 kDa glycoprotein unique among apolipoproteins because of its many functions, including the assembly, processing, and removal of plasma lipoproteins (5). It is a component of VLDL, intermediate-density lipoprotein, chylomicrons, HDL (6), and LDL (7). ApoE serves as a ligand for LDL receptors and, through its interaction with these receptors, participates in the transport of cholesterol and other lipids among various cells of the body (8). In humans, there are three common isoforms of apoE, apoE2, apoE3, and apoE4, with apoE3 being the most common isoform. ApoE4 differs from apoE3 by having an arginine at position 112, rather than the cysteine residue in apoE3 (9). The epsilon 4 allele is present in z25% of the population (10, 11) and linked to an increased risk for the development of atherosclerosis and Alzheimer's disease (12)(13)(14).ApoE contains a 22 kDa N-terminal domain (residues 1-191) and a 10 kDa C-terminal domain (residues 222-299) spaced by a protease-sensitive loop (15). The N-terminal domain contains the LDL receptor-binding region (residues 136-150 in helix 4), and the C-terminal domain has a high affinity for lipid and is responsible for lipoprotein lipid binding (16). Among the human isoforms, apoE4 shows a unique domain interaction in which the arginine at position 112 induces an interaction of arginine-61 in the N-terminal domain with glutamate-255 in the C-terminal domain, a feature thought to be responsible for the preferential association of apoE4 with VLDL...