A general approach was developed for the regio-and chemoselective covalent immobilization of soluble proteins on glass surfaces through an unnatural amino acid created by posttranslationally modifying the cysteine residue in a CaaX recognition motif with functional groups suitable for "click" chemistry or a Staudinger ligation. Farnesyl diphosphate analogs bearing ω-azide or ω-alkyne moieties were attached to the cysteine residue in Cys-Val-Ile-Ala motifs at the C-termini of engineered versions of green fluorescent protein (GFP) and glutathione S-transferase (GST) by protein farnesyltransferase. The derivatized proteins were attached to glass slides bearing linkers containing azide ("click" chemistry) or phosphine (Staudinger ligation) groups. "Click" immobilized proteins were detected by fluorescently labeled antibodies and remained attached to the slide through two cycles of stripping under stringent conditions at 80 °C. GFP immobilized by a Staudinger ligation was detected by directly imagining the GFP fluorophore over a period of 6 days. These methods for covalent immobilization of proteins should be generally applicable. CaaX recognition motifs can easily be appended to the C-terminus of a cloned protein by a simple modification of the corresponding gene, and virtually any soluble protein or peptide bearing a CaaX motif is a substrate for protein farnesyltransferase.Protein "chips" are useful for studying protein-ligand and protein-protein interactions, i including the detection of antibody-antigen interactions, ii and permit high-throughput screening of limited quantities of analytes in a microarray format. iii Devices with covalently attached proteins 1,iv are more robust than their non-covalent counterparts. v In addition, substantial enhancements in sensitivity are seen when proteins are attached in a uniform manner. 4,5,vi Typically covalent immobilization is accomplished by reactions that rely on nucleophilic moieties found in the side chains of naturally occurring amino acids. i,vii We now report a general approach for the regio-and chemoselective covalent immobilization of soluble proteins on glass surfaces through an unnatural amino acid created by posttranslationally modifying a cysteine residue with functional groups suitable for "click" chemistry viii or a Staudinger ligation. ix Protein farnesyltransferase (PFTase) catalyzes the alkylation of the sulfhydryl moiety in the cysteine located in C-terminal CaaX motifs, where X = A, S, M, or Q, by farnesyl diphosphate (1) (see Scheme 1). x The reaction is general for any soluble protein bearing a CaaX motif. We synthesized farnesyl analogs 2 and 3, both of which are excellent alternate substrates for yeast PFTase with catalytic efficiencies (1.6 and 0.58 µM −1 s −1 ) similar to that of 1 (0.76 µM −1 s −1 ). xi As model proteins for immobilization, we engineered C-terminal CVIA motifs into green fluorescent protein (GFP) and glutathione S-transferase (GST) proteins with azide analog 2 or alkyne analog 3 gave GFP-N 3 , GFP-C 2 , GST-N 3 , or G...

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BackgroundThe search for novel chemical entities targeting essential and parasite-specific pathways is considered a priority for neglected diseases such as trypanosomiasis and leishmaniasis. The thiol-dependent redox metabolism of trypanosomatids relies on bis-glutathionylspermidine [trypanothione, T(SH)2], a low molecular mass cosubstrate absent in the host. In pathogenic trypanosomatids, a single enzyme, trypanothione synthetase (TryS), catalyzes trypanothione biosynthesis, which is indispensable for parasite survival. Thus, TryS qualifies as an attractive drug target candidate.Methodology/Principal FindingA library composed of 144 compounds from 7 different families and several singletons was screened against TryS from three major pathogen species (Trypanosoma brucei, Trypanosoma cruzi and Leishmania infantum). The screening conditions were adjusted to the TryS´ kinetic parameters and intracellular concentration of substrates corresponding to each trypanosomatid species, and/or to avoid assay interference. The screening assay yielded suitable Z’ and signal to noise values (≥0.85 and ~3.5, respectively), and high intra-assay reproducibility. Several novel chemical scaffolds were identified as low μM and selective tri-tryp TryS inhibitors. Compounds displaying multi-TryS inhibition (N,N'-bis(3,4-substituted-benzyl) diamine derivatives) and an N5-substituted paullone (MOL2008) halted the proliferation of infective Trypanosoma brucei (EC50 in the nM range) and Leishmania infantum promastigotes (EC50 = 12 μM), respectively. A bis-benzyl diamine derivative and MOL2008 depleted intracellular trypanothione in treated parasites, which confirmed the on-target activity of these compounds.Conclusions/SignificanceNovel molecular scaffolds with on-target mode of action were identified as hit candidates for TryS inhibition. Due to the remarkable species-specificity exhibited by tri-tryp TryS towards the compounds, future optimization and screening campaigns should aim at designing and detecting, respectively, more potent and broad-range TryS inhibitors.

Proper cholesterol transport is crucial for the functionality of cells. In C. elegans, certain cholesterol derivatives called dafachronic acids (DAs) govern the entry into diapause. In their absence, worms form a developmentally arrested dauer larva. Thus, cholesterol transport to appropriate places for DA biosynthesis warrants the reproductive growth. Recently, we discovered a novel class of glycosphingolipids, PEGCs, required for cholesterol mobilization/transport from internal storage pools. Here, we identify other components involved in this process. We found that strains lacking polyunsaturated fatty acids (PUFAs) undergo increased dauer arrest when grown without cholesterol. This correlates with the depletion of the PUFA-derived endocannabinoids 2-arachidonoyl glycerol and anandamide. Feeding of these endocannabinoids inhibits dauer formation caused by PUFAs deficiency or impaired cholesterol trafficking (e.g. in Niemann-Pick C1 or DAF-7/TGF-β mutants). Moreover, in parallel to PEGCs, endocannabinoids abolish the arrest induced by cholesterol depletion. These findings reveal an unsuspected function of endocannabinoids in cholesterol trafficking regulation.

Eleven farnesyl diphosphate analogues, which contained ω-azide or alkyne substituents suitable for bioorthogonal Staudinger and Huisgen [3+2] cycloaddition coupling reactions, were synthesized. The analogues were evaluated as substrates for alkylation of peptide co-substrates by yeast protein farnesyl transferase. Five of the diphosphates were good alternative substrates for FPP. Steady-state kinetic constants were measured for the active compounds, and the products were characterized by HPLC and LC-Mass. Two of the analogues gave steady state kinetic parameters (k cat and K M ) very similar to those of the natural substrate.

We have synthesized new derivatives of the macrolide antibiotics erythromycin and azithromycin. Novel deoxysugar moieties were attached to these standard antibiotics by biotransformation using a heterologous host. The resulting compounds were tested against several standard laboratory and clinically isolated bacterial strains. In addition, they were also tested in vitro against standard and drug-resistant strains of human malaria parasites (Plasmodium falciparum) and the liver stages of the rodent malaria parasite (Plasmodium berghei). Antibacterial activity of modified erythromycin and azithromycin showed no improvement over the unmodified macrolides, but the modified compounds showed a 10-fold increase in effectiveness after a short-term exposure against blood stages of malaria. The new compounds also remained active against azithromycin-resistant strains of P. falciparum and inhibited growth of liver-stage parasites at concentrations similar to those used for primaquine. Our findings show that malaria parasites have two distinct responses to macrolide antibiotics, one reflecting the prokaryotic origin of the apicoplast and a second, as-yet uncharacterized response that we attribute to the eukaryotic nature of the parasite. This is the first report for macrolides that target two different functions in the Plasmodium parasites.

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