Immune surveillance via self digestion

The adaptive immune system is orchestrated by CD4+ T cells. These cells detect peptides presented on Major Histocompatibility Complex (MHC) class II molecules, which are loaded in late endosomes with products of lysosomal proteolysis. One pathway by which proteins gain access to degradation in lysosomes is macroautophagy. We recently showed that constitutive macroautophagy can be detected in cells relevant for the immune system, including dendritic cells. In these antigen presenting cells, autophagosomes frequently fused with MHC class II antigen loading compartments and targeting of Influenza matrix protein 1 (MP1) for macroautophagy enhanced MHC class II presentation to MP1-specific CD4+ T cell clones up to 20 fold. Our findings indicate that macroautophagy is a constitutive and efficient pathway of antigen delivery for MHC class II presentation. We suggest that this pathway samples intracellular proteins for immune surveillance and induction of tolerance in CD4+ T cells, and could be targeted for improved MHC class II presentation of vaccine antigens.     

Spatiotemporal modeling of first and second wave outbreak dynamics of COVID-19 in Germany

The COVID-19 pandemic has kept the world in suspense for the past year. In most federal countries such as Germany, locally varying conditions demand for state- or county-level decisions to adapt to the disease dynamics. However, this requires a deep understanding of the mesoscale outbreak dynamics between microscale agent models and macroscale global models. Here, we use a reparameterized SIQRD network model that accounts for local political decisions to predict the spatiotemporal evolution of the pandemic in Germany at county resolution. Our optimized model reproduces state-wise cumulative infections and deaths as reported by the Robert Koch Institute and predicts the development for individual counties at convincing accuracy during both waves in spring and fall of 2020. We demonstrate the dominating effect of local infection seeds and identify effective measures to attenuate the rapid spread. Our model has great potential to support decision makers on a state and community politics level to individually strategize their best way forward during the months to come.

     

The hypertrehalosaemic neuropeptide conformational twins of cicadas consist of only l-amino acids: are they cis–trans isomers?

Amino Acids - It is known for almost 25 years that the corpora cardiaca (neurosecretory glands) of cicadas synthesize two isobaric peptides with hypertrehalosaemic activity denominated...     

Detection of focal source and arrhythmogenic substrate from body surface potentials to guide atrial fibrillation ablation

Focal sources (FS) are believed to be important triggers and a perpetuation mechanism for paroxysmal atrial fibrillation (AF). Detecting FS and determining AF sustainability in atrial tissue can help guide ablation targeting. We hypothesized that sustained rotors during FS-driven episodes indicate an arrhythmogenic substrate for sustained AF, and that non-invasive electrical recordings, like electrocardiograms (ECGs) or body surface potential maps (BSPMs), could be used to detect FS and AF sustainability. Computer simulations were performed on five bi-atrial geometries. FS were induced by pacing at cycle lengths of 120–270 ms from 32 atrial sites and four pulmonary veins. Self-sustained reentrant activities were also initiated around the same 32 atrial sites with inexcitable cores of radii of 0, 0.5 and 1 cm. FS fired for two seconds and then AF inducibility was tested by whether activation was sustained for another second. ECGs and BSPMs were simulated. Equivalent atrial sources were extracted using second-order blind source separation, and their cycle length, periodicity and contribution, were used as features for random forest classifiers. Longer rotor duration during FS-driven episodes indicates higher AF inducibility (area under ROC curve = 0.83). Our method had accuracy of 90.6±1.0% and 90.6±0.6% in detecting FS presence, and 93.1±0.6% and 94.2±1.2% in identifying AF sustainability, and 80.0±6.6% and 61.0±5.2% in determining the atrium of the focal site, from BSPMs and ECGs of five atria. The detection of FS presence and AF sustainability were insensitive to vest placement (±9.6%). On pre-operative BSPMs of 52 paroxysmal AF patients, patients classified with initiator-type FS on a single atrium resulted in improved two-to-three-year AF-free likelihoods (p-value < 0.01, logrank tests). Detection of FS and arrhythmogenic substrate can be performed from ECGs and BSPMs, enabling non-invasive mapping towards mechanism-targeted AF treatment, and malignant ectopic beat detection with likely AF progression.     

Disease‐linked TDP‐43 hyperphosphorylation suppresses TDP‐43 condensation and aggregation

Post‐translational modifications (PTMs) have emerged as key modulators of protein phase separation and have been linked to protein aggregation in neurodegenerative disorders. The major aggregating protein in amyotrophic lateral sclerosis and frontotemporal dementia, the RNA‐binding protein TAR DNA‐binding protein (TDP‐43), is hyperphosphorylated in disease on several C‐terminal serine residues, a process generally believed to promote TDP‐43 aggregation. Here, we however find that Casein kinase 1δ‐mediated TDP‐43 hyperphosphorylation or C‐terminal phosphomimetic mutations reduce TDP‐43 phase separation and aggregation, and instead render TDP‐43 condensates more liquid‐like and dynamic. Multi‐scale molecular dynamics simulations reveal reduced homotypic interactions of TDP‐43 low‐complexity domains through enhanced solvation of phosphomimetic residues. Cellular experiments show that phosphomimetic substitutions do not affect nuclear import or RNA regulatory functions of TDP‐43, but suppress accumulation of TDP‐43 in membrane‐less organelles and promote its solubility in neurons. We speculate that TDP‐43 hyperphosphorylation may be a protective cellular response to counteract TDP‐43 aggregation.     

Chicken avidin exhibits pseudo-catalytic properties. Biochemical, structural, and electrostatic consequences

Avidin and its bacterial analogue streptavidin exhibit similarly high affinities toward the vitamin biotin. The extremely high affinity of these two proteins has been utilized as a powerful tool in many biotechnological applications. Although avidin and streptavidin have similar tertiary and quaternary structures, they differ in many of their properties. Here we show that avidin enhances the alkaline hydrolysis of biotinyl p-nitrophenyl ester, whereas streptavidin protects this reaction even under extreme alkaline conditions (pH > 12). Unlike normal enzymatic catalysis, the hydrolysis reaction proceeds as a single cycle with no turnover because of the extremely high affinity of the protein for one of the reaction products (i.e. free biotin). The three-dimensional crystal structures of avidin (2 A) and streptavidin (2.4 A) complexed with the amide analogue, biotinyl p-nitroanilide, as a model for the p-nitrophenyl ester, revealed structural insights into the factors that enhance or protect the hydrolysis reaction. The data demonstrate that several molecular features of avidin are responsible for the enhanced hydrolysis of biotinyl p-nitrophenyl ester. These include the nature of a decisive flexible loop, the presence of an obtrusive arginine 114, and a newly formed critical interaction between lysine 111 and the nitro group of the substrate. The open conformation of the loop serves to expose the substrate to the solvent, and the arginine shifts the p-nitroanilide moiety toward the interacting lysine, which increases the electron withdrawing characteristics and consequent electrophilicity of the carbonyl group of the substrate. Streptavidin lacked such molecular properties, and analogous interactions with the substrate were consequently absent. The information derived from these structures may provide insight into the action of artificial protein catalysts and the evolution of catalytic sites in general.     

Biotin induces tetramerization of a recombinant monomeric avidin. A model for protein-protein interactions

Chicken avidin, a homotetramer that binds four molecules of biotin was converted to a monomeric form by successive mutations of interface residues to alanine. The major contribution to monomer formation was the mutation of two aspartic acid residues, which together account for ten hydrogen bonding interactions at the 1-4 interface. Mutation of these residues, together with the three hydrophobic residues at the 1-3 interface, led to stable monomer formation in the absence of biotin. Upon addition of biotin, the monomeric avidin reassociated to the tetramer, which exhibited properties similar to those of native avidin, with respect to biotin binding, thermostability, and protease resistance. To our knowledge, these unexpected results represent the first example of a small monovalent ligand that induces oligomerization of a monomeric protein. This study may suggest a biological role for low molecular weight ligands in inducing oligomerization and in maintaining the stability of multimeric protein assemblies.     

Untersuchungen über die Wuchs- und Hemmstoffe der Wurzelspitze und der Plumula vonVicia faba

Zusammenfassung Wurzelspitzen und Plumulastückchen vonVicia faba-Keimlingen wurden auf ihren Wuchs- und Hemmstoffgehalt untersucht. Durch die Wuchsstoff-Präparate, die mittels der Agar-Abfangmethode aus Wurzelspitzen gewonnen worden waren, konnte im Haferkrümmungstest (mit unter- und überoptimaler IES-Zugabe zu den Präparaten) neben Wuchsstoff ein Hemmstoff nachgewiesen werden, der vermutlich nicht durch Wuchsstoffverdrängung von den plasmatischen Wirkorten angreift.Die Ergebnisse der Abfangversuche an Plumulastückchen zeigen diesen Hemmstoff nicht, lassen aber auf die Anwesenheit eines von IES verschiedenen Wuchsstoffes schließen.Die in Wurzelspitzen und Plumulae vonVicia faba-Keimlingen vorliegenden Wuchs- und Hemmstoffe wurden papierchromatographisch untersucht. Zur Auswertung der Ergebnisse wurden der Haferkrümmungstest, der Zylinder-Zuwachstest und der Wurzelspitzen-Zuwachstest herangezogen.Übereinstimmend konnte sowohl in Wurzelspitzen als auch in Plumulastückchen bei Chromatographie mit n-Butanol—Aqua bidest.—Ammoniak außer IES ein weiterer Wuchsstoff mit demR _f von 0,65 bis 0,75 nachgewiesen werden. Außerdem ist die Anwesenheit eines Wuchsstoffes mit einemR _f von 0,85–0,9 in beiden Organen zu vermuten. In Wurzelspitzen liegt bei einemRf von 0,1 ein weiterer Wuchsstoff vor, der als accelerator (nachBennet-Clark undKefford 1953) gedeutet wurde und der, im Gegensatz zur IES, eine stark wachstumsfördernde Wirkung auf Wurzelspitzen ausübt.Deutliche Hemmwirkungen auf Koleoptilzylinder wurden bei Plumula-und Wurzelspitzen-Extrakten durch Zonen mit demR _f von 0,45 erzielt. Es dürfte sich hierbei um den vonBennet-Clark undKefford (1953) beschriebenen inhibitor handeln. AufFaba-Wurzelspitzen wirkt dieser Stoff jedoch nicht hemmend.Als weiterer in Wurzelspitzen gebildeter Hemmstoff war eine Substanz mit demR _f von 0,65–0,75 zu vermuten.Mit 8 TextabbildungenTeil einer Dissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Hamburg.