Long-term intracellular symbiosis (or endosymbiosis) is widely distributed across invertebrates and is recognized as a major driving force in evolution. However, the maintenance of immune homeostasis in organisms chronically infected with mutualistic bacteria is a challenging task, and little is known about the molecular processes that limit endosymbiont immunogenicity and host inflammation. Here, we investigated peptidoglycan recognition protein (PGRP)-encoding genes in the cereal weevilSitophilus zeamais’s association withSodalis pierantoniusendosymbiont. We discovered that weevilpgrp-lbgenerates three transcripts via alternative splicing and differential regulation. A secreted isoform is expressed in insect tissues under pathogenic conditions through activation of the PGRP-LC receptor of the immune deficiency pathway. In addition, cytosolic and transmembrane isoforms are permanently produced within endosymbiont-bearing organ, the bacteriome, in a PGRP-LC–independent manner. Bacteriome isoforms specifically cleave the tracheal cytotoxin (TCT), a peptidoglycan monomer released by endosymbionts.pgrp-lbsilencing by RNAi results in TCT escape from the bacteriome to other insect tissues, where it chronically activates the host systemic immunity through PGRP-LC. While such immune deregulations did not impact endosymbiont load, they did negatively affect host physiology, as attested by a diminished sexual maturation of adult weevils. Whereaspgrp-lbwas first described in pathogenic interactions, this work shows that, in an endosymbiosis context, specific bacteriome isoforms have evolved, allowing endosymbiont TCT scavenging and preventing chronic endosymbiont-induced immune responses, thus promoting host homeostasis.

Docosahexaenoic acid (DHA) is the main essential omega-3 fatty acid in brain tissues required for normal brain development and function. An alteration of brain DHA in neurodegenerative diseases such as Alzheimer's and Parkinson's is observed. Targeted intake of DHA to the brain could compensate for these deficiencies. Blood DHA is transported across the blood-brain barrier more efficiently when esterified at the sn-2 position of lyso-phosphatidylcholine. We used a structured phosphatidylcholine to mimic 2-docosahexaenoyl-lysoPC (lysoPC-DHA), named AceDoPC (1-acetyl,2-docosahexaenoyl-glycerophosphocholine), that may be considered as a stabilized form of the physiological lysoPC-DHA and that is neuroprotective in experimental ischemic stroke. The aim of the present study was to investigate whether AceDoPC is a relevant delivery form of DHA to the brain in comparison with other forms of the fatty acid. By combining in vitro and in vivo experiments, our findings report for the first time that AceDoPC is a privileged and specific carrier of DHA to the brain, when compared with DHA-containing PC and non-esterified DHA. We also show that AceDoPC was hydrolyzed, in part, into lysoPC-DHA. Ex vivo autoradiography of rat brain reveals that DHA from AceDoPC was localized in specific brain regions playing key roles in memory, thoughts, and cognitive functions. Finally, using molecular modeling approaches, we demonstrate that electrostatic and lipophilic potentials are distributed very similarly at the surfaces of AceDoPC and lysoPC-DHA. Our findings identify AceDoPC as an efficient way to specifically target DHA to the brain, which would allow potential preventive and therapeutic approaches for neurological diseases.

The hydrophobic cavity of Lipid Transfer Protein 1 from Nicotiana tabacum is investigated in detail by NMR using xenon as a spy. The analysis of the (129)Xe chemical shifts and self-relaxation times gives evidence of protein-xenon interaction. Thermodynamics of the binding is characterized through the study of aliphatic (1)H and (13)C chemical shift variation as a function of xenon pressure. The binding constant is evaluated to 75.5 +/- 1.0 M(-1) at 293 K. The location of xenon inside the cavity is deduced from SPINOE experiments. The noble gas appears to occupy four sites, and xenon self-relaxation experiments indicate that it quickly jumps between different sites. The chemical shifts of amide protons and nitrogens also depend on the xenon concentration, either specifically or nonspecifically for atoms at the external surface of the protein. Yet, contrary to aliphatic atoms, they do not correspond to short-range interactions as confirmed by magnetization transfer experiments between laser-polarized xenon and protons in H(2)O. These (15)N chemical shift variations, used in combination with (15)N transverse self-relaxation rates to determine the lower limit of the binding rate, consequently reveal subtle changes in the structure of the protein upon binding.

PA1b (pea albumin 1, subunit b) is a small and compact 37-amino acid protein, isolated from pea seeds (Pisum sativum), that adopts a cystine knot fold. It acts as a potent insecticidal agent against major pests in stored crops and vegetables, making it a promising bioinsecticide. Here, we investigate the influence of individual residues on the structure and bioactivity of PA1b. A collection of 13 PA1b mutants was successfully chemically synthesized in which the residues involved in the definition of PA1b amphiphilic and electrostatic characteristics were individually replaced with an alanine. The three-dimensional structure of PA1b was outstandingly tolerant of modifications. Remarkably, receptor binding and insecticidal activities were both dependent on common well defined clusters of residues located on one single face of the toxin, with Phe-10, Arg-21, Ile-23, and Leu-27 being key residues of the binding interaction. The inactivity of the mutants is clearly due to a change in the nature of the side chain rather than to a side effect, such as misfolding or degradation of the peptide, in the insect digestive tract. We have shown that a hydrophobic patch is the putative site of the interaction of PA1b with its binding site. Overall, the mutagenesis data provide major insights into the functional elements responsible for PA1b entomotoxic properties and give some clues toward a better understanding of the PA1b mode of action.

The solution structure of termicin from hemocytes of the termite Pseudacanthotermes spiniger was determined by proton two-dimensional nuclear magnetic resonance spectroscopy and molecular modeling techniques. Termicin is a cysteine-rich antifungal peptide also exhibiting a weak antibacterial activity. The global fold of termicin consists of an ␣-helical segment (Phe4-Gln14) and a two-stranded (Phe19-Asp25 and Gln28-Phe33) antiparallel ␤-sheet forming a "cysteine stabilized ␣␤ motif" (CS␣␤) also found in antibacterial and antifungal defensins from insects and from plants. Interestingly, termicin shares more structural similarities with the antibacterial insect defensins and with MGD-1, a mussel defensin, than with the insect antifungal defensins such as drosomycin and heliomicin. These structural comparisons suggest that global fold alone does not explain the difference between antifungals and antibacterials. The antifungal properties of termicin may be related to its marked hydrophobicity and its amphipatic structure as compared to the antibacterial defensins. [SWISS-PROT accession number: Termicin (P82321); PDB accession number: 1MM0.]

South Africa is a country with a high incidence of tuberculosis (TB), complicated by coinfection with human immunodeficiency virus (HIV). The Xpert MTB/RIF (Cepheid, Sunnyvale, CA, USA) is used in South Africa as the test for the initial diagnosis of TB, and other molecular platforms such as the m2000 (Abbott Molecular, Des Plaines, IL, USA) are widely used for molecular monitoring of HIV load. The latter platform is now also equipped with the RealTime (RT) MTB and RealTime MTB RIF/INH assays for TB and first-line drug resistance screening but has not been evaluated in settings of HIV and TB coinfection. A prospective clinical validation study was conducted at a community health center in Johannesburg, South Africa, and consenting individuals with presumptive pulmonary TB were enrolled. The performance of the Abbott assays was compared with those of the Xpert MTB/RIF, liquid culture, drug susceptibility testing, and clinical case definitions. A statistical analysis was performed on 206 individuals (73% were HIV positive). The sensitivity and specificity of the RT MTB were 82.5% (confidence interval [CI], 67.2 to 92.7) and 93.1% (CI, 86.2 to 97.2) on raw sputum and 77.5% (CI, 61.5 to 89.2) and 95.1% (CI, 88.9 to 98.4) on concentrated sputum, respectively, compared with those from liquid culture. The RT MTB correctly identified 17/35 more smear-negative culture-positive specimens than the Xpert MTB/RIF. Both the RT MTB and the Xpert MTB/RIF displayed sensitivities Ͼ70% and specificities Ͼ90% in HIV-positive individuals. The available drug resistance results concurred with MTBDRplus and drug susceptibility profiles. The RT MTB assay has similar diagnostic performance to the Xpert MTB/RIF and is suited to testing presumptive TB patients coinfected with HIV. The existing laboratory information system connectivity, training, and technical support make this a viable polyvalent option to scale up TB alongside HIV laboratory testing services in South Africa.

PA1b (Pea Albumin 1, subunit b) is a peptide extract from pea seeds showing significant insecticidal activity against certain insects, such as cereal weevils (genus Sitophilus), the mosquitoes Culex pipiens and Aedes aegyptii, and certain species of aphids. PA1b has great potential for use on an industrial scale and for use in organic farming: it is extracted from a common plant; it is a peptide (and therefore suitable for transgenic applications); it can withstand many steps of extraction and purification without losing its activity; and it is present in a seed regularly consumed by humans and mammals without any known toxicity or allergenicity. The potential of this peptide to limit pest damage has stimulated research concerning its host range, its mechanism of action, its three-dimensional structure, the natural diversity of PA1b and its structure-function relationships.

Beetles thriving on tyrosine-poor diet sources often develop mutualistic associations with endosymbionts able to synthesize aromatic amino acids. This surplus of aromatic amino acids is used to reinforce the insect’s protective cuticle.