Comparative study of the N-glycoprotein synthesis through dolichol intermediates in mitochondria, Golgi apparatus-rich fraction and endoplasmic reticulum-rich fraction

The Cytotoxic Cardiac Glycoside (-)-Cryptanoside A from the Stems of Cryptolepis dubia and Its Molecular Targets

A cardiac glycoside epoxide, (-)-cryptanoside A (1), was isolated from the stems of Cryptolepis dubia collected in Laos, for which the complete structure was confirmed by analysis of its spectroscopic and single-crystal X-ray diffraction data, using copper radiation at a low temperature. This cardiac glycoside epoxide exhibited potent cytotoxicity against several human cancer cell lines tested, including HT-29 colon, MDA-MB-231 breast, OVCAR3 and OVCAR5 ovarian cancer, and MDA-MB-435 melanoma cells, with the IC50 values found to be in the range 0.1-0.5 μM, which is comparable with that observed for digoxin. However, it exhibited less potent activity (IC50 1.1 μM) against FT194 benign/nonmalignant human fallopian tube secretory epithelial cells when compared with digoxin (IC50 0.16 μM), indicating its more selective activity toward human cancer versus benign/nonmalignant cells. (-)-Cryptanoside A (1) also inhibited Na+/K+-ATPase activity and increased the expression of Akt and the p65 subunit of NF-κB but did not show any effects on the expression of PI3K. A molecular docking profile showed that (-)-cryptanoside A (1) binds to Na+/K+-ATPase, and thus 1 may directly target Na+/K+-ATPase to mediate its cancer cell cytotoxicity.

High-throughput profiling of the mitochondrial proteome using affinity fractionation and automation

Recent studies have demonstrated the need for complementing cellular genomic information with specific information on expressed proteins, or proteomics, since the correlation between the two is poor. Typically, proteomic information is gathered by analyzing samples on two-dimensional gels with the subsequent identification of specific proteins of interest by using trypsin digestion and mass spectrometry in a process termed peptide mass fingerprinting. These procedures have, as a rule, been labor-intensive and manual, and therefore of low throughput. The development of automated proteomic technology for processing large numbers of samples simultaneously has made the concept of profiling entire proteomes feasible at last. In this study, we report the initiation of the (eventual) complete profile of the rat mitochondrial proteome by using high-throughput automated equipment in combination with a novel fractionation technique using minispin affinity columns. Using these technologies, approximately one hundred proteins could be identified in several days. In addition, separate profiles of calcium binding proteins, glycoproteins, and hydrophobic or membrane proteins could be generated. Because mitochondrial dysfunction has been implicated in numerous diseases, such as cancer, Alzheimer's disease and diabetes, it is probable that the identification of the majority of mitochondrial proteins will be a beneficial tool for developing drug and diagnostic targets for associated diseases.

Phosphatidylserine translocation into brain mitochondria: involvement of a fusogenic protein associated with mitochondrial membranes

Data reported in the literature indicate that lipid movement between intracellular organelles can occur through contacts and close physical association of membranes (Vance, J.E. 1990. J Biol Chem 265: 7248-7256). The advantage of this mechanism is that the direct interaction of membranes provides the translocation event without the involvement of lipid-transport systems. However, pre-requisite for the functioning of this machinery is the presence of protein factors controlling membrane association and fusion. In the present work we have found that liposomes fuse to mitochondria at acidic pH and that the pre-treatment of mitochondria with pronase inhibits the fusogenic activity. Mixing of 14C-phosphatidylserine (PS) labeled liposomes with mitochondria at pH 6.0 results in the translocation of 14C-PS into mitochondria and in its decarboxylation to 14C-phosphatidylethanolamine through the PS decarboxylase activity localized on the outer surface of the inner mitochondrial membrane. Incorporation of 14C-PS is inhibited by the pre-treatment of mitochondria with pronase or with EEDQ, a reagent for the derivatization of the protonated form of carboxylic groups. These results indicate the presence of a protein associated with mitochondria which is able to trigger the fusion of liposomes to the mitochondrial membrane. A partial purification of a mitochondrial fusogenic glycoprotein is described in this work. The activity of the fusogenic protein appears to be dependent on the extent of protonation of the residual carboxylic groups and is influenced by the glucidic moiety, as demonstrated by its interaction with Concanavalin A. The purified protein is able to promote the recover of the 14C-PS import from liposomes to pronase-treated mitochondria. Therefore, the protein is candidate to be an essential component in the machinery for the mitochondrial import of PS.

Role of environmental conditions on the expression levels, glycoform pattern and levels of sialyltransferase for hFSH produced by recombinant CHO cells

A recombinant CHO cell line in which the expression of human follicle stimulating hormone (hFSH) was under the control of the beta actin promoter was maintained in steady state perfusion cultures on a protein free medium. The level of expression of the hFSH was controlled by varying the steady state level of dissolved oxygen (10-90% of air saturation) and of sodium butyrate (0-1.5mM). Under these conditions, the specific productivity of hFSH (qFSH) varied from 0.7 to 4.8 ng hFSH/10(6) cells/h. As the specific productivity of hFSH increased, there was a shift in the FSH isoforms to the lower pI fractions, corresponding to increased sialic acid content. As the specific productivity of hFSH increased, shifting the isoform distribution towards the lower pI isoforms, that the sialyltransferase enzymic activity also increased.