Arginase 1, an enzyme induced by Th2 cytokines, is a hallmark of alternatively activated macrophages and is responsible for the hydrolysis of L-arginine into ornithine, the building block for the production of polyamines. Upregulation of arginase 1 has been observed in a variety of diseases, but the mechanisms by which arginase contributes to pathology are not well understood. We reveal here a unique role for arginase 1 in the pathogenesis of nonhealing leishmaniasis, a prototype Th2 disease, and demonstrate that the activity of this enzyme promotes pathology and uncontrolled growth of Leishmania parasites in vivo. Inhibition of arginase activity during the course of infection has a clear therapeutic effect, as evidenced by markedly reduced pathology and efficient control of parasite replication. Despite the clear amelioration of the disease, this treatment does not alter the Th2 response. To address the underlying mechanisms, the arginase-induced L-arginine catabolism was investigated and the results demonstrate that arginase regulates parasite growth directly by affecting the polyamine synthesis in macrophages.

Bicyclams are a novel class of antiviral compounds which act as potent and selective inhibitors of the replication of human immunodeficiency virus type 1 (HIV-1) and HIV-2. They block an early step in the viral life cycle following adsorption to the CD4 receptor and preceding reverse transcription. To identify the molecular target of these compounds, we genetically analyzed variants of the HIV-1 molecular clone NL4-3, which developed resistance against two structurally related bicyclams, JM2763 and the more potent SID791. The resistant strains were obtained after long-term passaging in MT-4 cells in the presence of progressively increasing compound concentrations. Recombinants between selected genes of the resistant strains and the parental NL4-3 provirus were generated by adapting the marker rescue technique to MT-4 cells. The bicyclamresistant phenotype was rescued by transferring the envelope gp120 gene of bicyclam-resistant virus into the NL4-3 parental genetic background. In the gp120 genes of the resistant strains, we identified several mutations leading to amino acid substitutions in the V3 loop. Furthermore, two substitutions of highly conserved amino acids in close proximity to the disulfide bridges of the V3 and V4 loops were found in both SID791-and JM2763-resistant strains. Additional mutations in regions encoding V3, C4, V5, and C5 were present in SID791-resistant viruses. Recombination experiments with overlapping parts of the envelope gene indicated that most, if not all, of the mutations were necessary to develop the fully SID791 resistant phenotype. The mutations in the C-terminal part of gp120 downstream of the V3 loop sequence conferred partial resistance to JM2763 but did not significantly decrease susceptibility to SID791. The genetic data and the biological properties of the resistant viruses point to inhibition of entry and fusion as the mode of action of the HIV-inhibitory bicyclams. A possible mechanism of binding of bicyclams to gp120 leading to inhibition of unfolding of gp120 and its shedding from the gp41 fusion domain is discussed.

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RNAs contain post-transcriptional modifications, which fulfill a variety of functions in translation, secondary structure stabilization and cellular stress survival. Here, 2-methylthiocytidine (ms2C) is identified in tRNA of E. coli and P. aeruginosa using NAIL-MS (nucleic acid isotope labeling coupled mass spectrometry) in combination with genetic screening experiments. ms2C is only found in 2-thiocytidine (s2C) containing tRNAs, namely tRNAArgCCG, tRNAArgICG, tRNAArgUCU and tRNASerGCU at low abundances. ms2C is not formed by commonly known tRNA methyltransferases. Instead, we observe its formation in vitro and in vivo during exposure to methylating agents. More than half of the s2C containing tRNA can be methylated to carry ms2C. With a pulse-chase NAIL-MS experiment, the repair mechanism by AlkB dependent sulfur demethylation is demonstrated in vivo. Overall, we describe ms2C as a bacterial tRNA modification and damage product. Its repair by AlkB and other pathways is demonstrated in vivo by our powerful NAIL-MS approach.

The outcome of Leishmania major infection in IL-4-deficient BALB/c mice has been a controversial subject. We have shown that IL-4-deficient BALB/c mice infected with Leishmania major developed progressive lesions and could not contain the replication of the parasites, whereas other studies have reported that IL-4-deficient mice were able to resist infection. Therefore, we examined different factors that can influence the course of Leishmania major infection. We tested different lines of IL-4-deficient BALB/c mice and show that the reported differences in the outcome of infection were not due to the different genetic origin of the embryonic stem cells used to disrupt the IL-4 gene. In addition, we infected IL-4-deficient mice with different isolates of L. major parasites and show that none of the parasite strains tested were cleared, although some of them caused milder pathology. Interestingly, this milder pathology was paralleled by a reduced arginase activity of the parasites. We also tested the influence of age on the course of Leishmania major infection in IL-4-deficient BALB/c mice and show that older mice express a transient resistance. Thus, we conclude that differences in the age of the mice and in the arginase activity of the different isolates of parasites are factors that can influence the non-healing phenotype of IL-4-/- BALB/c mice.

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Gold nanoshells, with a silica core and different core and shell dimensions, have been extensively investigated. Optical far-field properties, namely extinction and absorption, have been separately determined by means of spectrophotometry and photoacoustic spectroscopy, respectively, in the 440-900 nm range. The enhancement factor for surface-enhanced Raman scattering, which is related to near-field effects, has been measured from 568 to 920 nm. The absorption contribution to extinction decreases as the overall diameter increases. Moreover, absorption and scattering display different spectral distributions, the latter being red shifted. The Surface Enhanced Raman Scattering enhancement profile, measured using thiobenzoic acid as a Raman probe, is further shifted to the red. The latter result suggests that the enhancement is dominated by the presence of hot spots, which are possibly related to the surface roughness of gold nanoshell particles.

In all domains of life, the nucleobases of tRNA can be methylated. These methylations are introduced either by enzymes or by the reaction of methylating agents with the nucleophilic centers of the nucleobases. Herein, we present a systematic approach to identify the methylation sites within RNA in vitro and in vivo. For discrimination between enzymatic tRNA methylation and tRNA methylation damage in bacteria, we used nucleic acid isotope labeling coupled mass spectrometry (NAIL‐MS). With NAIL‐MS, we clearly observed the formation of 7‐methylguanosine, 3‐methyluridine, and 6‐methyladenosine during exposure of bacteria to the alkylating agent methyl methanesulfonate (MMS) in vivo. These damage products were not reported to form in tRNA in vivo, as they were masked by the enzymatically formed modified nucleosides in previous studies. In addition, we found formation of the known damage products 1‐methyladenosine and 3‐methylcytidine in vivo. With a dynamic NAIL‐MS setup, we observed tRNA repair by demethylation of these two RNA modifications in vivo. Furthermore, we saw the potential repair of 6‐methyladenosine but not 7‐methylguanosine in bacterial tRNA.