Identification and characterization of a phage display-derived peptide for orthopoxvirus detection.

Fast and reliable diagnostic assays are required for a resilient detection of clinical infections or biothreat-relevant pathogens. While PCR has proven to be the gold standard for nucleic acid detection, the identification of pathogen particles is still challenging and depends on the availability of well-characterized, chemically stable, and selective recognition molecules. Here, we report the screening of a phage display random peptide library for vaccinia virus-binding peptides. The identified peptide was extensively characterized using peptide-probe ELISA, surface plasmon resonance, nLC-MS/MS, Western Blot, peptide-based immunofluorescence assay, and electron microscopy. Following identification, the phage-free, synthetic peptide, designated αVACVpep05, was shown to bind to vaccinia virus and other orthopoxviruses. We can demonstrate that the highly conserved orthopoxvirus surface protein D8 is the interaction partner of αVACVpep05, thus enabling the peptide to bind to other orthopoxviruses, including cowpox virus and monkeypox virus, viruses that cause clinically relevant zoonotic infections in humans. The process of phage display-mediated peptide identification has been optimized intensively, and we provide recommendations for the identification of peptides suitable for the detection of further pathogens. The peptide described here was critically characterized and seems to be a promising reagent for the development of diagnostic platforms for orthopoxviruses. We believe that our results will help to promote the development of alternative, nonantibody-based synthetic detection molecules for further pathogens.

Leishmania Encodes a Bacterium-like 2,4-Dienoyl-Coenzyme A Reductase That Is Required for Fatty Acid ß-Oxidation and Intracellular Parasite Survival.

Leishmania spp. are protozoan parasites that cause a spectrum of important diseases in humans. These parasites develop as extracellular promastigotes in the digestive tract of their insect vectors and as obligate intracellular amastigotes that infect macrophages and other phagocytic cells in their vertebrate hosts. Promastigote-to-amastigote differentiation is associated with marked changes in metabolism, including the upregulation of enzymes involved in fatty acid ß-oxidation, which may reflect adaptation to the intracellular niche. Here, we have investigated the function of one of these enzymes, a putative 2,4-dienoyl-coenzyme A (CoA) reductase (DECR), which is specifically required for the ß-oxidation of polyunsaturated fatty acids. The Leishmania DECR shows close homology to bacterial DECR proteins, suggesting that it was acquired by lateral gene transfer. It is present in other trypanosomatids that have obligate intracellular stages (i.e., Trypanosoma cruzi and Angomonas) but is absent from dixenous parasites with an exclusively extracellular lifestyle (i.e., Trypanosoma brucei). A DECR-green fluorescent protein (GFP) fusion protein was localized to the mitochondrion in both promastigote and amastigote stages, and the levels of expression increased in the latter stages. A Leishmania major Δdecr null mutant was unable to catabolize unsaturated fatty acids and accumulated the intermediate 2,4-decadienoyl-CoA, confirming DECR's role in ß-oxidation. Strikingly, the L. major Δdecr mutant was unable to survive in macrophages and was avirulent in BALB/c mice. These findings suggest that ß-oxidation of polyunsaturated fatty acids is essential for intracellular parasite survival and that the bacterial origin of key enzymes in this pathway could be exploited in developing new therapies.IMPORTANCE The Trypanosomatidae are protozoan parasites that infect insects, plants, and animals and have evolved complex monoxenous (single host) and dixenous (two hosts) lifestyles. A number of species of Trypanosomatidae, including Leishmania spp., have evolved the capacity to survive within intracellular niches in vertebrate hosts. The adaptations, metabolic and other, that are associated with development of intracellular lifestyles remain poorly defined. We show that genomes of Leishmania and Trypanosomatidae that can survive intracellularly encode a 2,4-dienoyl-CoA reductase that is involved in catabolism of a subclass of fatty acids. The trypanosomatid enzyme shows closest similarity to the corresponding bacterial enzymes and is located in the mitochondrion and essential for intracellular growth of Leishmania The findings suggest that acquisition of this gene by lateral gene transfer from bacteria by ancestral monoxenous Trypanosomatidae likely contributed to the development of a dixenous lifestyle of these parasites.