Proteomic analysis of melanoma-derived exosomes by two-dimensional polyacrylamide gel electrophoresis and mass spectrometry

Exosomes are 40-100 nm vesicles released by numerous cell types and are thought to have a variety of roles depending on their origin. Exosomes derived from antigen presenting cells have been shown to be capable of initiating immune responses in vivo and eradicating established tumours in murine models. Tumour-derived exosomes can be utilised as a source of tumour antigen for cross-priming to T-cells and are thus of interest for use in anti-tumour immunotherapy. Further exploration into the protein composition of exosomes may increase our understanding of their potential roles in vivo and this study has examined the proteome of exosomes purified from cell supernatants of the melanoma cell lines MeWo and SK-MEL-28. The vesicular nature and size (30-100 nm) of the purified exosomes was confirmed by electron microscopy and sucrose density gradient centrifugation. Western blotting demonstrated the absence of calnexin and cytochrome c, verifying the purity of the exosome preparations, as well as enrichment of MHC class I and the tumour-associated antigens Mart-1 and Mel-CAM. The two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) protein profiles of exosomes from the two cell lines were highly comparable and strikingly different from the profiles of the total cell lysates. Mass spectrometric sequencing identified proteins present in 49 protein spots in the exosome lysates. Several of these have been identified previously in exosomes but some are novel, including p120 catenin, radixin, and immunoglobulin superfamily member 8 (PGRL). Proteins present in whole-cell lysates that were significantly reduced or excluded from exosomes were also identified and included several mitochondrial and lysosomal proteins, again confirming the proposed endosomal origin of exosomes. This study presents a starting point for future more in-depth protein studies of tumour-derived exosomes which will aid the understanding of their biogenesis and targeting for use in anti-tumour immunotherapy protocols.     

Discovery of dipiperidines as new antitubercular agents

As part of our ongoing research effort to develop new therapeutics for treatment of tuberculosis (TB), we synthesized a combinatorial library of 10,358 compounds on solid support using a pool-and-split technique and tested the resulting compounds for activity against Mycobacterium tuberculosis. Structure–activity relationship (SAR) evaluation identified new compounds with antitubercular activity, including a novel hit series that is structurally unrelated to any existing antitubercular drugs, dipiperidines. Dipiperidine representatives exhibited MIC values as low as 7.8 μM, the ability to induce promoter Rv0341 activated in response to cell wall biosynthesis inhibition, relatively low nonspecific cellular toxicity in the range of 30–162 μM, and log P values less than 4.     

Substituted azaquinazolinones as modulators of GHSr-1a for the treatment of type II diabetes and obesity

Substituted azaquinazolinones were identified as antagonists of the GHSr-1A receptor for the treatment of type II diabetes and obesity. Optimisation for potency and LogD lead to the identification of orally bioavailable, potent antagonists with improved selectivity over hERG.     

Lizard herbivory in a sand dune environment: the diet of Angolosaurus skoogi

Summary Early observations of the feeding habits of Angolosaurus skoogi (Andersson), a 50–120 g lizard inhabiting the almost vegetationless dunes of the northern Namib Desert, indicated that this species was herbivorous. Less than two percent of living lizard species are predominantly herbivorous and these species tend to have a high body mass (>100 g). We therefore analysed fecal pellets of A. skoogi to obtain dietary details of this relatively rare lizard. Eighteen food taxa were identified: 81 percent by mass was composed of vegetable matter, of which 56 percent was an endemic, perennial cucurbit Acanthosicyos horrida. Both spatial and temporal variation in dietary composition were apparent. Ready access to water in the form of A. horrida is postulated to have allowed Angolosaurus to occupy this extreme habitat and to forage on components of the windblown detritus, a food source that would probably not be usable in other circumstances.     

Mutagenesis identifies amino acid residues in extracellular loops and within the barrel lumen that determine voltage gating of porin from Haemophilus influenzae type b.

Porin (341 amino acids; M(r) 37 782) of Haemophilus influenzae type b mediates exchange of solutes between the external environment and the periplasm of this Gram-negative bacterium. Positively charged residues in the extracellular loops have been shown to be involved in the voltage gating of this protein. To further elucidate our observations on the functional properties of this channel, we mutated seven lysines (Lys(48), Lys(161), Lys(165), Lys(170), Lys(248), Lys(250), and Lys(253)) to glutamic acid. The selected residues were previously shown to be accessible to chemical modification, and they map to three locations: loop 4 and loop 6, and within the barrel lumen. The seven mutant proteins were purified, and each was reconstituted into planar lipid bilayers to characterize its channel forming properties. The single substitution mutant porins displayed increased single channel conductances in 1 M KCl ranging between 134 and 178% of the single channel conductance for wild-type Hib porin. Six of the seven mutant porins also displayed altered current-voltage relationships when compared to wild-type Hib porin. Whereas Lys(170)Glu had activity similar to wild-type Hib porin, Lys(48)Glu, Lys(248)Glu, and Lys(253)Glu showed substantial voltage gating at both positive and negative polarities. Lys(161)Glu and Lys(250)Glu gated only at negative potentials, and Lys(165)Glu gated only at positive potentials. Rather than ascribing one specific loop in gating, our analyses of these mutant Hib porins suggest that voltage gating can be attributed to contributions from loops 4 and 6 and a residue within the barrel lumen.