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Fatty acid-and retinol-binding proteins (FARs) belong to a unique family of excreted/secreted proteins (ESPs) found exclusively in nematodes. Much of our understanding of these proteins, however, is limited to their in vitro binding characteristics toward various fatty acids and retinol and has provided little insight into their in vivo functions or mechanisms. Recent research, however, has shown that FARs elicit an immunomodulatory role in plant and animal model systems, likely by sequestering lipids involved in immune signaling. This alludes to the intricate relationship between parasitic nematode effectors and their hosts.

Parasitic nematodes cause significant morbidity and mortality globally. Excretory/secretory products (ESPs) such as fatty acid- and retinol- binding proteins (FARs) are hypothesized to suppress host immunity during nematode infection, yet little is known about their interactions with host tissues. Leveraging the insect parasitic nematode, Steinernema carpocapsae, we describe here the first in vivo study demonstrating that FARs modulate animal immunity, causing an increase in susceptibility to bacterial co-infection. Moreover, we show that FARs dampen key components of the fly immune response including the phenoloxidase cascade and antimicrobial peptide (AMP) production. Our data also reveal that FARs deplete lipid signaling precursors in vivo as well as bind to these fatty acids in vitro, suggesting that FARs elicit their immunomodulatory effects by altering the availability of lipid signaling molecules necessary for an efficient immune response. Collectively, these data support a complex role for FARs in immunosuppression in animals and provide detailed mechanistic insight into parasitism in phylum Nematoda.

BackgroundLeptospirosis, a re-emerging disease of global importance caused by pathogenic Leptospira spp., is considered the world's most widespread zoonotic disease. Rats serve as asymptomatic carriers of pathogenic Leptospira and are critical for disease spread. In such reservoir hosts, leptospires colonize the kidney, are shed in the urine, persist in fresh water and gain access to a new mammalian host through breaches in the skin.Methodology/principal findingsPrevious studies have provided evidence for post-translational modification (PTM) of leptospiral proteins. In the current study, we used proteomic analyses to determine the presence of PTMs on the highly abundant leptospiral protein, LipL32, from rat urine-isolated L. interrogans serovar Copenhageni compared to in vitro-grown organisms. We observed either acetylation or tri-methylation of lysine residues within multiple LipL32 peptides, including peptides corresponding to regions of LipL32 previously identified as epitopes. Intriguingly, the PTMs were unique to the LipL32 peptides originating from in vivo relative to in vitro grown leptospires. The identity of each modified lysine residue was confirmed by fragmentation pattern analysis of the peptide mass spectra. A synthetic peptide containing an identified tri-methylated lysine, which corresponds to a previously identified LipL32 epitope, demonstrated significantly reduced immunoreactivity with serum collected from leptospirosis patients compared to the peptide version lacking the tri-methylation. Further, a subset of the identified PTMs are in close proximity to the established calcium-binding and putative collagen-binding sites that have been identified within LipL32.Conclusions/significanceThe exclusive detection of PTMs on lysine residues within LipL32 from in vivo-isolated L. interrogans implies that infection-generated modification of leptospiral proteins may have a biologically relevant function during the course of infection. Although definitive determination of the role of these PTMs must await further investigations, the reduced immune recognition of a modified LipL32 epitope suggests the intriguing possibility that LipL32 modification represents a novel mechanism of immune evasion within Leptospira.

Interleukin-6 (IL-6) is an immunoregulatory cytokine that activates a cell-surface signaling assembly composed of IL-6, the IL-6 α-receptor (IL-6Rα), and the shared signaling receptor gp130. The 3.65 angstrom-resolution structure of the extracellular signaling complex reveals a hexameric, interlocking assembly mediated by a total of 10 symmetry-related, thermodynamically coupled interfaces. Assembly of the hexameric complex occurs sequentially: IL-6 is first engaged by IL-6Rα and then presented to gp130 in the proper geometry to facilitate a cooperative transition into the high-affinity, signaling-competent hexamer. The quaternary structures of other IL-6/IL-12 family signaling complexes are likely constructed by means of a similar topological blueprint., Gp130 is a shared signal-transducing receptor for a family of more than 10 different four-helix-bundle cytokines, including IL-6, leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), oncostatin-M (OSM), and others [...]

The active site of copper-containing nitrite reductase (NiR), the carbonyl derivatives of the wild-type enzyme and the Asp98Asn variant are studied by Fourier transform infrared (FTIR) spectroscopy. NiR from Alcaligenes faecalis (AfNiR) is a trimeric multi-copper enzyme.Z

The lytB gene of Escherichia coli encodes a protein that contributes in the regulation of guanosine 3'5'-bispyrophosphate metabolism. The gene is also involved in temperature sensitivity as well as penicillin tolerance. A fragment of the lytB gene is used as a probe to determine the occurrence of similar genes in other bacteria. Southern blot studies revealed that similar genes are present among gram-negative bacteria.

The lipid kinase PI4KB, which generates phosphatidylinositol 4‐phosphate (PI4P), is a key enzyme in regulating membrane transport and is also hijacked by multiple picornaviruses to mediate viral replication. PI4KB can interact with multiple protein binding partners, which are differentially manipulated by picornaviruses to facilitate replication. The protein c10orf76 is a PI4KB‐associated protein that increases PI4P levels at the Golgi and is essential for the viral replication of specific enteroviruses. We used hydrogen–deuterium exchange mass spectrometry to characterize the c10orf76‐PI4KB complex and reveal that binding is mediated by the kinase linker of PI4KB, with formation of the heterodimeric complex modulated by PKA‐dependent phosphorylation. Complex‐disrupting mutations demonstrate that PI4KB is required for membrane recruitment of c10orf76 to the Golgi, and that an intact c10orf76‐PI4KB complex is required for the replication of c10orf76‐dependent enteroviruses. Intriguingly, c10orf76 also contributed to proper Arf1 activation at the Golgi, providing a putative mechanism for the c10orf76‐dependent increase in PI4P levels at the Golgi. Synopsis: Enteroviruses hijack host PI4KB and GBF1 to build replication organelles. This study reveals that the direct interaction between c10orf76 and PI4KB is required for c10orf76 recruitment to the Golgi and the replication of c10orf76‐dependent enteroviruses. c10orf76 is localized to the Golgi through a direct interaction with the kinase linker of PI4KB.c10orf76 regulates GBF1 and active Arf1 dynamics that control Golgi PI4P levels.Enteroviruses that rely on c10orf76 for replication depend on formation of the c10orf76‐PI4KB complex. [ABSTRACT FROM AUTHOR]