Arabidopsis PAP17 is a dual-localized purple acid phosphatase up-regulated during phosphate deprivation, senescence, and oxidative stress.

A 35 kDa monomeric purple acid phosphatase (APase) was purified from cell wall extracts of Pi starved (-Pi) Arabidopsis thaliana suspension cells and identified as AtPAP17 (At3g17790) by mass spectrometry and N-terminal microsequencing. AtPAP17 was de novo synthesized and dual-localized to the secretome and/or intracellular fraction of -Pi or salt-stressed plants, or senescing leaves. Transiently expressed AtPAP17-green fluorescent protein localized to lytic vacuoles of the Arabidopsis suspension cells. No significant biochemical or phenotypical changes associated with AtPAP17 loss of function were observed in an atpap17 mutant during Pi deprivation, leaf senescence, or salinity stress. Nevertheless, AtPAP17 is hypothesized to contribute to Pi metabolism owing to its marked up-regulation during Pi starvation and leaf senescence, broad APase substrate selectivity and pH activity profile, and rapid repression and turnover following Pi resupply to -Pi plants. While AtPAP17 also catalyzed the peroxidation of luminol, which was optimal at pH 9.2, it exhibited a low Vmax and affinity for hydrogen peroxide relative to horseradish peroxidase. These results, coupled with absence of a phenotype in the salt-stressed or -Pi atpap17 mutant, do not support proposals that the peroxidase activity of AtPAP17 contributes to the detoxification of reactive oxygen species during stresses that trigger AtPAP17 up-regulation.

Mitochondria as central characters in a complex narrative: Linking genomics, energetics, pace-of-life, and aging in natural populations of garter snakes.

As a pacesetter for physiological processes, variation in metabolic rate can determine the shape of energetic trade-offs and thereby drive variation in life-history traits. In turn, such variation in metabolic performance and life-histories can have profound consequences for lifespan and lifetime fitness. Thus, the extent to which metabolic rate variation is due to phenotypic plasticity or fixed genetic differences among individuals or populations is likely to be shaped by natural selection. Here, we first present a generalized framework describing the central role of mitochondria in processes linking environmental, genomic, physiological, and aging variation. We then present a test of these relationships in an exemplary system: populations of garter snakes (Thamnophis elegans) exhibiting contrasting life-history strategies - fast-growing, early-reproducing, and fast-aging (FA) versus slow-growing, late-reproducing, and slow-aging (SA). Previous work has characterized divergences in mitochondrial function, reactive oxygen species processing, and whole-organism metabolic rate between these contrasting life-history ecotypes. Here, we report new data on cellular respiration and mitochondrial genomics and synthesize these results with previous work. We test hypotheses about the causes and implications of mitochondrial genome variation within this generalized framework. First, we demonstrate that snakes of the FA ecotype increase cellular metabolic rate across their lifespan, while the opposite pattern holds for SA snakes, implying that reduced energetic throughput is associated with a longer life. Second, we show that variants in mitochondrial genomes are segregating across the landscape in a manner suggesting selection on the physiological consequences of this variation in habitats varying in temperature, food availability, and rates of predation. Third, we demonstrate functional variation in whole-organism metabolic rate related to these mitochondrial genome sequence variants. With this synthesis of numerous datasets, we are able to further characterize how variation across levels of biological organization interact within this generalized framework and how this has resulted in the emergence of distinct life-history ecotypes that vary in their rates of aging and lifespan.

The Ins and Outs of Autophagic Ribosome Turnover.

Ribosomes are essential for protein synthesis in all organisms and their biogenesis and number are tightly controlled to maintain homeostasis in changing environmental conditions. While ribosome assembly and quality control mechanisms have been extensively studied, our understanding of ribosome degradation is limited. In yeast or animal cells, ribosomes are degraded after transfer into the vacuole or lysosome by ribophagy or nonselective autophagy, and ribosomal RNA can also be transferred directly across the lysosomal membrane by RNautophagy. In plants, ribosomal RNA is degraded by the vacuolar T2 ribonuclease RNS2 after transport by autophagy-related mechanisms, although it is unknown if a selective ribophagy pathway exists in plants. In this review, we describe mechanisms of turnover of ribosomal components in animals and yeast, and, then, discuss potential pathways for degradation of ribosomal RNA and protein within the vacuole in plants.

Mitochondria-acting hexokinase II peptides carried by short-length carbon nanotubes with increased cellular uptake, endosomal evasion, and enhanced bioactivity against cancer cells.

Type II hexokinase (HKII) has emerged as a viable therapeutic target due to its involvement in metabolic reprogramming and also apoptosis prevention. The peptide derived from the fifteen amino acid sequence in the HKII N-terminal region [HKII(pep)] can compete with endogenous proteins for binding on mitochondria and trigger apoptosis. However, this peptide is not cell-permeable. In this study, multi-walled carbon nanotubes (MWCNTs) were used to effectively deliver HKII(pep) across cellular barriers without compromising their bioactivity. The peptide was conjugated on either oxidized MWCNTs or 2,2'-(ethylenedioxy)bis(ethylamine)-functionalized MWCNTs, yielding MWCNT-HKII(pep) and MWCNT-TEG-HKII(pep), respectively. Both conjugates were shown to be internalized by breast cancer MCF-7 cells using confocal microscopy. Moreover, these nanoconjugates seemed to have escaped from endosomes and be in the vicinity of mitochondria. The WST-1 cytotoxicity assay conducted on MCF-7 and colon carcinoma HCT116 cells revealed that MWCNT-peptide conjugates were significantly more effective in curbing cancer cell growth compared to a commercially available cell permeable HKII fusion peptide. In addition, both nanoconjugates displayed an enhanced ability in eliciting apoptosis and depleting the ATP level in HCT116 cells compared to the mere HKII peptide. Importantly, hexokinase II release from mitochondria was demonstrated in MWCNT-HKII(pep) and MWCNT-TEG-HKII(pep) treated cells, highlighting that the structure and bioactivity of HKII(pep) were not compromised after covalent conjugation to MWCNTs.

The complete mitochondrial genome sequence of Onychostoma alticorpus (Cypriniformes, Cyprinidae).

We determined the complete mitochondrial genome (mitogenome) sequence of Onychostoma alticorpus, which is known as an endemic freshwater species in Taiwan, by using long polymerase chain reaction method. The total length of O. alticorpus mitogenome is 16,680 bp, consisting of 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs genes and a noncoding control region. The overall base composition of O. alticorpus is 30.88% for A, 23.57% for T, 16.56% for G and 28.99% for C, with a slight AT bias of 54.45%. Gene location and specific usage of distinct termination codon types characterize typically the vertebrate mitochondrial genome. The determination of O. alticorpus mitogenome would play an important role not only in the delineation of phylogeographic history and population genetic structure, but reflection of conservation efforts on the genetic diversity as well as population vitality.