Mislocalization of the exitatory amino-acid transporters (EAATs) in human astrocytoma and non-astrocytoma cancer cells: effect of the cell confluence

Background  

Astrocytomas are cancers of the brain in which high levels of extracellular glutamate plays a critical role in tumor growth and resistance to conventional treatments. This is due for part to a decrease in the activity of the glutamate transporters, i.e. the Excitatory Amino Acid Transporters or EAATs, in relation to their nuclear mislocalization in astrocytoma cells. Although non-astrocytoma cancers express EAATs, the localization of EAATs and the handling of L-glutamate in that case have not been investigated.     

Structure-function study of cathelicidin-derived bovine antimicrobial peptide BMAP-28: Design of its cell-selective analogs by amino acid substitutions in the heptad repeat sequences

Although BMAP-28 is a potent cathelicidin-derived bovine antimicrobial peptide, its cytotoxic activity against the human and other mammalian cells is of concern for converting it into a novel antimicrobial drug. We have identified a short leucine and isoleucine zipper sequences at the N- and C-terminals of BMAP-28, respectively. To understand the possible role of these structural elements in BMAP-28, a number of alanine-substituted analogs were designed, synthesized and characterized along with the wild-type peptide. The substitution of amino acids at single or multiple ‘a’ position(s) of these structural motifs by alanine showed significant effects on the cytotoxic activity of the molecule on the human red blood cells (hRBCs) and 3T3 cells without showing much effects on their MIC values against the selected bacteria. BMAP-28 and all its analogs depolarized the Escherichia coli cells with almost equal efficacy. In contrast, the alanine-substituted analogs of BMAP-28 depolarized hRBCs much less efficiently than the parent molecule. Results further showed that BMAP-28 assembled appreciably onto the live E. coli and hRBC. However, the selected less toxic analogs of BMAP-28 although assembled as good as the parent molecule onto the live E. coli cells, their assembly onto the live mammalian hRBCs was much weaker as compared to that of the wild-type molecule. Looking at the remarkable similarity with the data presented in our previous work on melittin, it appears that probably the heptad repeat sequence possesses a general role in maintaining the cytotoxicity of the antimicrobial peptides against the mammalian cells and assembly therein.     

DEVELOPMENT OF GENETICALLY ENCODED FLUORESCENT PROTEIN CONSTRUCTS OF HYPERTHERMOPHILIC MALTOSE-BINDING PROTEIN

Circularly permuted green fluorescent protein (cGFP) was inserted into the hyperthermophilic maltose binding protein at two different locations. cGFP was inserted between amino acid residues 206 and 207, or fused to the N-terminal of maltose binding protein from Thermotoga maritima. The cloned DNA constructs were expressed in Escherichia coli cells, and purified by metal chelate affinity chromatography. Conformational change upon ligand binding was monitored by the increase in fluorescence intensity. Both of the fusion proteins developed significant fluorescence change at 0.5 mM maltose concentration, whereas their maltose binding affinities and optimum incubation times were different. Fluorescent biosensors based on mesophilic maltose binding proteins have been described in the literature, but there is a growing interest in biosensors based on thermostable proteins. Therefore, the developed protein constructs could be models for thermophilic protein-based fluorescent biosensors.