The Autophagy Receptor TAX1BP1 (T6BP) improves antigen presentation by MHC‐II molecules

CD4⁺ T lymphocytes play a major role in the establishment and maintenance of immunity. They are activated by antigenic peptides derived from extracellular or newly synthesized (endogenous) proteins presented by the MHC‐II molecules. The pathways leading to endogenous MHC‐II presentation remain poorly characterized. We demonstrate here that the autophagy receptor, T6BP, influences both autophagy‐dependent and ‐independent endogenous presentation of HIV‐ and HCMV‐derived peptides. By studying the immunopeptidome of MHC‐II molecules, we show that T6BP affects both the quantity and quality of peptides presented. T6BP silencing induces the mislocalization of the MHC‐II‐loading compartments and rapid degradation of the invariant chain (CD74) without altering the expression and internalization kinetics of MHC‐II molecules. Defining the interactome of T6BP, we identify calnexin as a T6BP partner. We show that the calnexin cytosolic tail is required for this interaction. Remarkably, calnexin silencing replicates the functional consequences of T6BP silencing: decreased CD4⁺ T cell activation and exacerbated CD74 degradation. Altogether, we unravel T6BP as a key player of the MHC‐II‐restricted endogenous presentation pathway, and we propose one potential mechanism of action.     

Artenzusammensetzung,lichtgenuß und energiegehalt der krautschicht des Valdivianischen Regenwaldes bei St. Martin

Zusammenfassung Pflanzensoziologische Aufnahmen im Valdivianischen Regenwald bei St. Martin ergaben, daß dieser Wald als eine Variante des Nothofago-Perseetum zu betrachten ist, der sich durch zahlreiches Vorkommen von Aextoxicon punctatum auszeichnet. Nach dem Lebensformenspektrum dominieren die Phanerophyten, an zweiter Stelle stehen die Epiphyten, von denen die Hymenophyllen 30% ausmachen. Die Vielschichtigkeit des Valdivianischen Regenwaldes bedingt sehr unterschiedliche Lichtbedingungen. Nach der Lichtkartierung lassen sich Nertera granadensis, Seneclo cymosus und Chusquea quila als besonders lichtbedürftige Arten, Rhamnus diffusus, Lapageria rosea und Luzuriaga raticans als im Schatten wachsende Arten charakterisieren.Die Stoffgruppenanalyse ergab auffallend hohe Lipoidgehalte der Blätter: dieser hohe Anteil an Lipoiden und ätherischen Ölen dürfte weitgehend für den ebenfalls hohen Brennwert des Valdivianischen Regenwaldes verantwertlich sein, der nach der Analyse von 29 Arten errechnet wurde. Dieser Brennwert liegt welt über dem des tropischen Regenwaldes, stimmt dagegen fast mit demjenigen von Mischwäldern der gemäßlgten Zone überein. Charakteristisch hebt sich der Brennwert verschiedener Wuchsformen voneinander ab, wobei der Kalorienwert von den Gehölzen und Lianen zu den Epiphyten und weiter zur Krautschicht abfällt. Ein Vergleich der Brennwerte von Monocotylen und Dicotylen aus dem Valdivianischen Regenwald mit den entsprechenden Mittelwerten von Pflanzenmaterial anderer Regionen ergibt eine ziemlich gute Übereinstimmung, jedoch bestchen größere Differenzen, wenn sich der Vergieich auf die Brennwerte bestimmter Familien beschränkt.

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Summary Plant sociological mapping in the Valdivian rain forest near St. Martin/Chile led to the conelusion that this forest should be considered as a variant of the Nothofago-Perseetum with a high abundance of Aextoxicon punctatum. The spectrum of life forms shows clear dominance of phanerophytes, followed by epiphytes; 30% of these are Hymenophyllaceae. The multilayered system of strata within the forest causes quite different light conditions. Nertera granadensis, Senecio cymosus and Chusquea quila require optimal illumination; Rhamnus diffusus, Lapageria and Luzuriaga radicans on the contrary are satisfied with low light intensities in shady places.Analysis of the most important components of the leaves showed surprisingly high contents of lipolds; this and the etheric oils must be responsible for the likewise high caloric value of the Valdivian rain forest which was calculated as an average for 29 species. This average caloric value is far above that for tropical rain forest but almost agrees with that for mixed forests of the temperate zone. The fumigation value of various life forms differs characteristically: it declines from woody species (trees and bushes) plus lianes to epiphytes and to herbs. In a taxonomic comparison of caloric values of monocotyledons and dicotyledons the Valdivian rain forest agrees fairly well with the caloric value of plant material from other regions. However there are higher differences if the comparison of caloric values is limited to distinct plant families.

Prof. Dr. H. Walter zum 80. Geburtstag gewidmet.     

Uterine infusion of conceptus fragments changes the protein profile from cyclic mares

This experiment aimed to compare at day seven after ovulation, the protein profile of uterine fluid in cyclic mares with mares infused two days before with Day 13 conceptus fragments. Experimental animals were ten healthy cyclic mares, examined daily to detect ovulation (Day 0) as soon as estrus was confirmed. On day seven, after ovulation, uterine fluid was collected, constituting the Cyclic group (n = 10). The same mares were examined in the second cycle until ovulation was detected. On day five, after ovulation, fragments from a previously collected concepti were infused into each mare''s uterus. Two days after infusion, uterine fluid was collected, constituting the Fragment group (n = 10). Two-dimensional electrophoresis technique processed uterine fluid samples. A total of 373 spots were detected. MALDI-TOF/TOF and NanoUHPLC-QTOF mass spectrometry identified twenty spots with differences in abundance between the Cyclic and Fragment group. Thirteen proteins were identified, with different abundance between groups. Identified proteins may be related to embryo-maternal communication, which involves adhesion, nutrition, endothelial cell proliferation, transport, and immunological tolerance. In conclusion, conceptus fragments signalized changes in the protein profile of uterine fluid seven days after ovulation in comparison to the observed at Day 7 in the same cyclic mares.     

Export of the pneumococcal phage SV1 lysin requires choline‐containing teichoic acids and is holin‐independent

Streptococcus pneumoniae bacteriophages (phages) rely on a holin–lysin system to accomplish host lysis. Due to the lack of lysin export signals, it is assumed that holin disruption of the cytoplasmic membrane allows endolysin access to the peptidoglycan. We investigated the lysis mechanism of pneumococcal phage SV1, by using lysogens without holin activity. Upon phage induction in a holin deficient background, phage lysin was gradually targeted to the cell wall, in spite of lacking any obvious signal sequence. Our data indicate that export of the phage lysin requires the presence of choline in the teichoic acids, an unusual characteristic of pneumococci. At the bacterial surface, the exolysin remains bound to choline residues without inducing lysis, but is readily activated by the collapse of the membrane potential. Additionally, the activation of the major autolysin LytA, which also participates in phage‐mediated lysis, is equally related to perturbations of the membrane proton motive force. These results indicate that collapse of the membrane potential by holins is sufficient to trigger bacterial lysis. We found that the lysin of phage SV1 reaches the peptidoglycan through a novel holin‐independent pathway and propose that the same mechanism could be used by other pneumococcal phages.     

Anti-Inflammatory Effect of Targeted Delivery of SOD to Endothelium: Mechanism,Synergism with NO Donors and Protective Effects In Vitro and In Vivo

Pro-inflammatory activation of vascular endothelium is implicated in pathogenesis of severe conditions including stroke, infarction and sepsis. We have recently reported that superoxide dismutase (SOD) conjugated with antibodies (Ab/SOD) that provide targeted delivery into endothelial endosomes mitigates inflammatory endothelial activation by cytokines and agonists of Toll-like receptors (TLR). The goal of this study was to appraise potential utility and define the mechanism of this effect. Ab/SOD, but not non-targeted SOD injected in mice alleviated endotoxin-induced leukocyte adhesion in the cerebral vasculature and protected brain from ischemia-reperfusion injury. Transfection of endothelial cells with SOD, but not catalase inhibited NFκB signaling and expression of Vascular Cell Adhesion Molecule-1 induced by both cytokines and TLR agonists. These results affirmed that Ab/SOD-quenched superoxide anion produced by endothelial cells in response to proinflammatory agents mediates NFκB activation. Furthermore, Ab/SOD potentiates anti-inflammatory effect of NO donors in endothelial cells in vitro, as well as in the endotoxin-challenged mice. These results demonstrate the central role of intracellular superoxide as a mediator of pro-inflammatory activation of endothelium and support the notion of utility of targeted interception of this signaling pathway for management of acute vascular inflammation.     

Genetic distance of two fibrillar collagen loci, COL3A1 and COL5A2, located on the long arm of human chromosome 2

Two of the human fibrillar collagen genes, proa1(III) (COL3A1) and proa2(V) (COL5A2), map to the same region of the long arm of chromosome 2. To establish the genetic distance between the two loci, we analyzed the segregation of COL3A1 and COL5A2 RFLPs in five families informative for the two loci specific markers. We found that the maximum lod score was 9.33 at a recombination frequency of theta = 0.00. The data therefore provide strong evidence for tight linkage between two evolutionarily related fibrillar collagen genes on the 2q14----2q32 segment of chromosome 2.     

Strong magnesium binding sites in yeast phenylalanine transfer RNA.

To ascertain the sites that are available for strong binding between magnesium ions and phosphate groups in yeast phenylalanine transfer RNA, all distances below 5.5 A separating the phosphoryl oxygens (Op) of the 76 nucleotide residues have been computed from the latest atomic coordinates for the monoclinic form of the tRNA crystallized in the presence of magnesium chloride. The 5.5 A distance is chosen as the upper limit expected for Op....Op distances involved in strong magnesium-phosphate binding, on the basis of studies on a model magnesium phosphodiester hydrate, taking into account the quoted standard deviation in the tRNA atomic coordinates. It is concluded that there are four possible sites for strong magnesium binding in the tRNA molecule, in addition to the three sites previously reported. One of the hypothetical sites: m2G10-OL, U47-OR, could be involved in the first stage of melting of the tRNA molecule, and may be relevant to tertiary structure stabilization, since it links the dihydrouridine arm with the extra (V) loop.