Induction of alternative pathway respiration by nitrate in Chlamydomonas

Abstract Besides the ubiquitous cytochrome pathway of mitochondrial respiration, the green algae Chlamydomonas reinhardtii possesses an alternative pathway of respiration, which is comprised of a single protein, alternative oxidase (AOX). AOX is induced when C. reinhardtii cells are shifted from a growth medium containing ammonium as the nitrogen source to one with nitrate. The primary aim of this thesis was to understand the metabolic connections between nitrate assimilation and the induction of the alternative pathway. That these two metabolic processes are closely linked is supported by the fact that a gene encoding AOX (AOX1) is clustered with the genes required for nitrate assimilation (NAR genes). To investigate if the clustering of AOX1 with NAR genes occurs in other green algae, publicly available genome databases were searched. It was found that while the clustering of NAR genes is widespread in many lineages of green algae, the presence of AOX1 within a NAR cluster is a characteristic of only a single group of green algae, the chlorophytes. Interestingly, it was found that lineages that lack NAR gene clustering seem to have a preference for importing amino acids instead of nitrate as their dominant source of nitrogen. The role of AOX in nitrate assimilation was investigated by constitutively blocking AOX1 expression. AOX knockdown cells displayed a slightly decreased rate of growth and distinctly different photosynthetic electron transport characteristics. Whole-cell metabolite analysis showed that the lack of AOX in the mitochondrion in knockdown cells suppressed the stimulatory effect of nitrate on oxidative pentose phosphate pathway (oxPPP) activity within the chloroplast. Interestingly, this regulation also occurred in the opposite direction. In wild-type cells, the biochemical inhibition of oxPPP by glycerol in the chloroplast decreased the accumulation of AOX in the mitochondrion. Overall, the data suggests that the induction of AOX by nitrate relieves respiratory electron transport from adenylate control. During nitrate assimilation increased demand by the chloroplast for ATP would decrease the transfer of ADP and Pi to the mitochondria restricting the rate of the cytochrome pathway. Up regulation of the alternative pathway would allow for continued upstream respiratory carbon flow under limiting adenylate conditions. Keywords Alternative oxidase, nitrate, Chlamydomonas, respiration, oxidative pentose phosphate pathwa

Glycosylated notch and cancer

Glycosylation is one of the key components influencing several signaling pathways implicated in cell survival and growth. The Notch signaling pathway plays a pivotal role in numerous cell fate specifications during metazoan development. Both Notch and its ligands are repeatedly glycosylated by the addition of sugar moieties, such as O-fucose, O-glucose, or O-xylose, to bring about structural and functional changes. Disruption to glycosylation processes of Notch proteins result in developmental disorders and disease, including cancer. This review summarizes the importance and recent updates on the role of glycosylated Notch proteins in tumorigenesis and tumor metastasis

Bioresistive identification of heat shock protein 90

90 kDa heat shock protein (HSP90) is a ubiquitous molecular chaperone and is one of the abundant proteins present in a cell under normal and stressed conditions. The adenosine triphosphate (ATP) binding region of HSP90 is currently under a great degree of study because of the interest of its role in cancer and protein maintenance; the binding of ATP to HSP90 induces a large conformational change in the protein as a result of the activity of different types of stressors within the cells. In the present paper, a simple microfluidic biosensor is proposed for the characterization of ATP-HSP90 interactions through the principle of bioresistive variation. The experimental results prove that the present biosensor system is highly suitable for the detection of heat shock proteins present in a real-time biological sample, which is very useful for in-situ biomedical applications and rapid pathogenic detections