The use of styrene-maleic acid (SMA) copolymers to extract and purify transmembrane proteins, while retaining their native bilayer environment, overcomes many of the disadvantages associated with conventional detergent-based procedures. This approach has huge potential for the future of membrane protein structural and functional studies. In this investigation, we have systematically tested a range of commercially available SMA polymers, varying in both the ratio of styrene and maleic acid and in total size, for the ability to extract, purify and stabilise transmembrane proteins. Three different membrane proteins (BmrA, LeuT and ZipA), which vary in size and shape, were used. Our results show that several polymers, can be used to extract membrane proteins, comparably to conventional detergents. A styrene:maleic acid ratio of either 2:1 or 3:1, combined with a relatively small average molecular mass (7.5-10 kDa), is optimal for membrane extraction, and this appears to be independent of the protein size, shape or expression system. A subset of polymers were taken forward for purification, functional and stability tests. Following a one-step affinity purification, SMA 2000 was found to be the best choice for yield, purity and function. However, the other polymers offer subtle differences in size and sensitivity to divalent cations that may be useful for a variety of downstream applications.

Curcumin is a compound derived from the spice, tumeric. It is a potent inhibitor of the SERCA Ca 2þ pumps (all isoforms), inhibiting Ca 2þ -dependent ATPase activity with IC 50 values of between 7 and 15 mM. It also inhibits ATPdependent Ca 2þ -uptake in a variety of microsomal membranes, although for cerebellar and platelet microsomes, a stimulation in Ca 2þ uptake is observed at low curcumin concentrations (,10 mM). For the skeletal muscle isoform of the Ca 2þ pump (SERCA1), the inhibition of curcumin is noncompetitive with respect to Ca 2þ , and competitive with respect to ATP at high curcumin concentrations (< 10-25 mM). This was confirmed by ATP binding studies that showed inhibition in the presence of curcumin: ATP-dependent phosphorylation was also reduced. Experiments with fluorescein 5 0 -isothiocyanate (FITC)-labelled ATPase also suggest that curcumin stabilizes the E1 conformational state. The fact that FITC labels the nucleotide binding site of the ATPase (precluding ATP from binding), and the fact that curcumin affects FITC fluorescence indicate that curcumin must be binding to another site within the ATPase that induces a conformational change to prevent ATP from binding. This observation is interpreted, with the aid of recent structural information, as curcumin stabilizing the interaction between the nucleotidebinding and phosphorylation domains, precluding ATP binding.Keywords: SERCA; ATP binding; curcumin; phosphorylation; fluorescence.Tumeric is extensively used as a spice in Asian cooking and as a colouring agent in both the food and cosmetic industries [1]. Curcumin (diferuoylmethane or 1,7-bis(4-hydroxy-3-methoxyphenol)-1,6-heptadiene-3,5-dione) is a compound found in tumeric that gives it its distinctive yellow colour [2]. Recently it has been shown that curcumin has anticarcinogenic effects [3] that may be linked to its antioxidant properties [4]. Studies have shown that curcumin can affect a number of cellular processes including: activation of apoptosis in Jurkat T-cells [5], inhibition of platelet aggregation [6,7] and inhibition of inflammatory cytokine production in macrophages [8]. Curcumin has also been shown to affect the activity of a number of key enzymes such as cyclooxygenase [9], protein kinase C [10], protein tyrosine kinases [11] and a Ca 2þ -dependent endonuclease [12]. Many of these processes/enzymes are also known to be regulated by Ca 2þ .Cytosolic free Ca 2þ concentration ([Ca 2þ ] cyt ) is tightly controlled, due its importance in the regulation of many cellular processes. The sarco/endoplasmic reticulum Ca 2þ ATPase (SERCA) is one of the major mechanisms by which the low levels of [Ca 2þ ] cyt are maintained within cells. Three isoforms of the SERCA family of Ca 2þ pumps have so far been identified [13,14] and these are expressed in a tissuespecific manner [14]. SERCA1 is found predominantly in fast-twitch skeletal muscle while SERCA2a is found within cardiac and slow-twitch muscle. The splice variant form of SERCA2 (SERCA2b), which has an extended C-terminus is foun...

Resistance of cancer cells to chemotherapy is a significant clinical concern and mechanisms regulating cell death in cancer therapy, including apoptosis, autophagy or necrosis, have been extensively investigated over the last decade. Accordingly, the identification of medicinal compounds against chemoresistant cancer cells via new mechanism of action is highly desired. Autophagy is important in inducing cell death or survival in cancer therapy. Recently, novel autophagy activators isolated from natural products were shown to induce autophagic cell death in apoptosis-resistant cancer cells in a calcium-dependent manner. Therefore, enhancement of autophagy may serve as additional therapeutic strategy against these resistant cancers. By computational docking analysis, biochemical assays, and advanced live-cell imaging, we identified that neferine, a natural alkaloid from Nelumbo nucifera, induces autophagy by activating the ryanodine receptor and calcium release. With well-known apoptotic agents, such as staurosporine, taxol, doxorubicin, cisplatin and etoposide, utilized as controls, neferine was shown to induce autophagic cell death in a panel of cancer cells, including apoptosis-defective and -resistant cancer cells or isogenic cancer cells, via calcium mobilization through the activation of ryanodine receptor and Ulk-1-PERK and AMPK-mTOR signaling cascades. Taken together, this study provides insights into the cytotoxic mechanism of neferine-induced autophagy through ryanodine receptor activation in resistant cancers.

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