The physiological origin of task-evoked systemic artefacts in functional near infrared spectroscopy

A major methodological challenge of functional near-infrared spectroscopy (fNIRS) is its high sensitivity to haemodynamic fluctuations in the scalp. Superficial fluctuations contribute on the one hand to the physiological noise of fNIRS, impairing the signal-to-noise ratio, and may on the other hand be erroneously attributed to cerebral changes, leading to false positives in fNIRS experiments. Here we explore the localisation, time course and physiological origin of task-evoked superficial signals in fNIRS and present a method to separate them from cortical signals. We used complementary fNIRS, fMRI, MR-angiography and peripheral physiological measurements (blood pressure, heart rate, skin conductance and skin blood flow) to study activation in the frontal lobe during a continuous performance task. The General Linear Model (GLM) was applied to analyse the fNIRS data, which included an additional predictor to account for systemic changes in the skin. We found that skin blood volume strongly depends on the cognitive state and that sources of task-evoked systemic signals in fNIRS are co-localized with veins draining the scalp. Task-evoked superficial artefacts were mainly observed in concentration changes of oxygenated haemoglobin and could be effectively separated from cerebral signals by GLM analysis. Based on temporal correlation of fNIRS and fMRI signals with peripheral physiological measurements we conclude that the physiological origin of the systemic artefact is a task-evoked sympathetic arterial vasoconstriction followed by a decrease in venous volume. Since changes in sympathetic outflow accompany almost any cognitive and emotional process, we expect scalp vessel artefacts to be present in a wide range of fNIRS settings used in neurocognitive research. Therefore a careful separation of fNIRS signals originating from activated brain and from scalp is a necessary precondition for unbiased fNIRS brain activation maps.

Immune versus natural selection: antibody aldolases with enzymic rates but broader scope

Structural and mechanistic studies show that when the selection criteria of the immune system are changed, catalytic antibodies that have the efficiency of natural enzymes evolve, but the catalytic antibodies are much more accepting of a wide range of substrates. The catalytic antibodies were prepared by reactive immunization, a process whereby the selection criteria of the immune system are changed from simple binding to chemical reactivity. This process yielded aldolase catalytic antibodies that approximated the rate acceleration of the natural enzyme used in glycolysis. Unlike the natural enzyme, however, the antibody aldolases catalyzed a variety of aldol reactions and decarboxylations. The crystal structure of one of these antibodies identified the reactive lysine residue that was selected in the immunization process. This lysine is deeply buried in a hydrophobic pocket at the base of the binding site, thereby accounting for its perturbed pKa.

Observation of covalent intermediates in an enzyme mechanism at atomic resolution

In classical enzymology, intermediates and transition states in a catalytic mechanism are usually inferred from a series of biochemical experiments. Here, we derive an enzyme mechanism from true atomic-resolution x-ray structures of reaction intermediates. Two ultra-high resolution structures of wild-type and mutant d-2-deoxyribose-5-phosphate (DRP) aldolase complexes with DRP at 1.05 and 1.10 angstroms unambiguously identify the postulated covalent carbinolamine and Schiff base intermediates in the aldolase mechanism. In combination with site-directed mutagenesis and (1)H nuclear magnetic resonance, we can now propose how the heretofore elusive C-2 proton abstraction step and the overall stereochemical course are accomplished. A proton relay system appears to activate a conserved active-site water that functions as the critical mediator for proton transfer.

Experimental observation of the topological structure of exceptional points

We report on a microwave cavity experiment where exceptional points (EPs), which are square root singularities of the eigenvalues as function of a complex interaction parameter, are encircled in the laboratory. The real and imaginary parts of an eigenvalue are given by the frequency and width of a resonance and the eigenvectors by the field distributions. Repulsion of eigenvalues--always associated with EPs--implies frequency anticrossing (crossing) whenever width crossing (anticrossing) is present. The eigenvalues and eigenvectors are interchanged while encircling an EP, but one of the eigenvectors undergoes a sign change which can be discerned in the field patterns.

An antibody exo Diels-Alderase inhibitor complex at 1.95 angstrom resolution

A highly specific Diels-Alder protein catalyst was made by manipulating the antibody repertoire of the immune system. The catalytic antibody 13G5 catalyzes a disfavored exo Diels-Alder transformation in a reaction for which there is no natural enzyme counterpart and that yields a single regioisomer in high enantiomeric excess. The crystal structure of the antibody Fab in complex with a ferrocenyl inhibitor containing the essential haptenic core that elicited 13G5 was determined at 1.95 angstrom resolution. Three key antibody residues appear to be responsible for the observed catalysis and product control. Tyrosine-L36 acts as a Lewis acid activating the dienophile for nucleophilic attack, and asparagine-L91 and aspartic acid-H50 form hydrogen bonds to the carboxylate side chain that substitutes for the carbamate diene substrate. This hydrogen-bonding scheme leads to rate acceleration and also pronounced stereoselectivity. Docking experiments with the four possible ortho transition states of the reaction explain the specific exo effect and suggest that the (3R,4R)-exo stereoisomer is the preferred product.

MicroRNA-146a reduces MHC-II expression via targeting JAK/STAT signaling in dendritic cells after stem cell transplantation

Acute Graft-versus-host disease (GVHD) is a major immunological complication after allogeneic hematopoietic cell transplantation and a better understanding of the molecular regulation of the disease could help to develop novel targeted therapies. Here we found that a G/C polymorphism within the human microRNA-146a (miR-146a) gene of transplant-recipients, which causes reduced miR-146a levels, was strongly associated with the risk of developing severe acute GVHD (n=289). In mice, deficiency of miR-146a in the hematopoietic system or transfer of recipient-type miR 146a^-/- dendritic cells (DCs) enhanced GVHD, while miR-146a mimic-transfected-DCs ameliorated disease. Mechanistically, lack of miR-146a enhanced JAK2 STAT1-pathway activity, which led to higher expression of class II-transactivator (CIITA) and consecutively increased MHCII-levels on DCs. Inhibition of JAK1/2 or CIITA knockdown in DCs prevented miR-146a^-/- DC-induced GVHD exacerbation. Consistent with our findings in mice, patients with the miR-146a polymorphism rs2910164 in hematopoietic cells displayed higher MHCII levels on monocytes, which could be targeted by JAK1/2-inhibition.

Our findings indicate that the miR-146a polymorphism rs2910164 identifies patients at high risk for GVHD before allo HCT. Functionally we show that miR-146a acts as a central regulator of recipient-type DC activation during GVHD by dampening the pro-inflammatory JAK-STAT/CIITA/MHCII axis, which provides a scientific rationale for early JAK1/2-inhibition in selected patients.

First experimental evidence for chaos-assisted tunneling in a microwave annular billiard

We report on first experimental signatures for chaos-assisted tunneling in a two-dimensional annular billiard. Measurements of microwave spectra from a superconducting cavity with high frequency resolution are combined with electromagnetic field distributions experimentally determined from a normal conducting twin cavity with high spatial resolution to resolve eigenmodes with properly identified quantum numbers. Distributions of quasidoublet splittings serve as basic observables for the tunneling between whispering gallery-type modes localized to congruent, but distinct tori which are coupled weakly to irregular eigenstates associated with the chaotic region in phase space.

Displacement of disordered water molecules from hydrophobic pocket creates enthalpic signature: binding of phosphonamidate to the S₁'-pocket of thermolysin

BACKGROUND

Prerequisite for the design of tight binding protein inhibitors and prediction of their properties is an in-depth understanding of the structural and thermodynamic details of the binding process. A series of closely related phosphonamidates was studied to elucidate the forces underlying their binding affinity to thermolysin. The investigated inhibitors are identical except for the parts penetrating into the hydrophobic S₁'-pocket.

METHODS

A correlation of structural, kinetic and thermodynamic data was carried out by X-ray crystallography, kinetic inhibition assay and isothermal titration calorimetry.

RESULTS AND CONCLUSIONS

Binding affinity increases with larger ligand hydrophobic P₁'-moieties accommodating the S₁'-pocket. Surprisingly, larger P₁'-side chain modifications are accompanied by an increase in the enthalpic contribution to binding. In agreement with other studies, it is suggested that the release of largely disordered waters from an imperfectly hydrated pocket results in an enthalpically favourable integration of these water molecules into bulk water upon inhibitor binding. This enthalpically favourable process contributes more strongly to the binding energetics than the entropy increase resulting from the release of water molecules from the S₁'-pocket or the formation of apolar interactions between protein and inhibitor.

GENERAL SIGNIFICANCE

Displacement of highly disordered water molecules from a rather imperfectly hydrated and hydrophobic specificity pocket can reveal an enthalpic signature of inhibitor binding.

Observation of a chiral state in a microwave cavity

A microwave experiment has been realized to measure the phase difference of the oscillating electric field at two points inside the cavity. The technique has been applied to a dissipative resonator which exhibits a singularity-called exceptional point-in its eigenvalue and eigenvector spectrum. At the singularity, two modes coalesce with a phase difference of pi/2. We conclude that the state excited at the singularity has a definitive chirality.

Engagement of the Fc epsilon RI stimulates the production of IL-16 in Langerhans cell-like dendritic cells

Preferential uptake and presentation of IgE-bound allergens by epidermal Langerhans cells (LC) via the high affinity IgE receptor, FcepsilonRI, is regarded as an important mechanism in the induction of cutaneous inflammation in atopic dermatitis. Here, we show that activation of monocyte-derived LC-like dendritic cells (LLDC) through engagement of FcepsilonRI induces the expression of IL-16, a chemoattractant factor for dendritic cells, CD4+ T cells, and eosinophils. We found that ligation of FcepsilonRI on LLDC derived from atopic dermatitis patients that express high levels of FcepsilonRI increases IL-16 mRNA expression and storage of intracellular IL-16 protein and enhances the secretion of mature IL-16 in a biphasic manner. An early release of IL-16 (peak at 4 h) is independent of protein synthesis, while a more delayed release (peak at 12 h) requires protein synthesis and occurs subsequent to the induction of IL-16 mRNA and intracellular accumulation of pro-IL-16. There was evidence that LLDC use caspase-1 to process IL-16, as inhibition of caspase-1, but not of caspase-3, partially prevented the release of IL-16 in response to ligation of FcepsilonRI. In an in vivo model of IgE-dependent LC activation, the atopy patch test, positive skin reactions were also associated with the induction of IL-16 in epidermal dendritic cells. These data indicate that IL-16 released from LC after allergen-mediated activation through FcepsilonRI may link IgE-driven and cellular inflammatory responses in diseases such as atopic dermatitis.

Encircling an exceptional point

We calculate analytically the geometric phases that the eigenvectors of a parametric dissipative two-state system described by a complex symmetric Hamiltonian pick up when an exceptional point (EP) is encircled. An EP is a parameter setting where the two eigenvalues and the corresponding eigenvectors of the Hamiltonian coalesce. We show that it can be encircled on a path along which the eigenvectors remain approximately real and discuss a microwave cavity experiment, where such an encircling of an EP was realized. Since the wave functions remain approximately real, they could be reconstructed from the nodal lines of the recorded spatial intensity distributions of the electric fields inside the resonator. We measured the geometric phases that occur when an EP is encircled four times and thus confirmed that for our system an EP is a branch point of fourth order.

Structure of octreotide, a somatostatin analogue

Octreotide, a synthetic somatostatin analogue, is an octapeptide with one disulfide bridge. Crystals of octreotide are orthorhombic, space group P2(1)2(1)2(1), a = 18.458 (5), b = 30.009 (7), c = 39.705 (27) A, with three molecules of octapeptide, one ordered oxalate dianion and 52 water molecules in the asymmetric unit. Complete protonation of the NH(2) groups (as assumed in the refinement) would require three oxalate dianions in the asymmetric unit for charge neutrality; a chemical analysis indicated that four are present. In either case they are so disordered that they cannot be distinguished from the water molecules. The 18 951 unique reflections (R(sym) = 0.026) used for structure solution and refinement were recorded with the EMBL imaging-plate scanner using synchrotron radiation. The structure was solved by Patterson interpretation, locating the three disulfide bridges, followed by tangent phase expansion and E-Fourier recycling. The anisotropic refinement against all F(2) data between 1.04 and 10.0 A resolution by blocked restrained full-matrix least-squares techniques converged to a conventional R index based on F of 0.084 [I > 2a(I) and 10.0 > d > 1.04 A] and wR2, the weighted R-index on F(2), of 0.246 (for all data). One peptide molecule adopts a flat beta-sheet structure; the other two possess different irregular backbone conformations, but are similar to each other. All three molecules have a distorted type II' beta-turn around the D-Trp-Lys region, but exhibit different side-chain conformations. The crystal structure is stabilized by a network of inter- and intramolecular hydrogen bonds.

Development of Hemolytic Anemia in a Nivolumab-Treated Patient with Refractory Metastatic Squamous Cell Skin Cancer and Chronic Lymphatic Leukemia

Management of patients with metastatic squamous cell skin cancer, refractory to initial therapy with standard chemotherapy and radiation protocols, remains difficult with poor overall prognosis and limited therapeutic options. Recently, promising response rates with nivolumab, a programmed death receptor-1-blocking antibody, in squamous cancer of the head and neck have been demonstrated. Considering the similar histological patterns of squamous cell cancer of the skin and squamous cell cancer of the head and neck, we assumed that nivolumab could also be effective in our patients with refractory metastatic squamous cell cancer of the skin. So far, there have been no clinical data on the therapeutic efficacy of nivolumab in squamous cell skin cancer. We here present a case of a patient with metastatic squamous cell skin cancer refractory to previous therapies, who showed a good response to nivolumab over a period of 5 months, but developed a serious hemolytic crisis under nivolumab treatment after eight applications.

Crystal structure of a cocaine-binding antibody

Murine monoclonal antibody GNC92H2 was elicited by active immunization with a cocaine immunoconjugate and binds free cocaine with excellent specificity and moderate affinity. Improvement of affinity, as well as humanization of GNC92H2, would be advantageous in immunopharmacotherapy for cocaine addiction, and for emergency cases of drug overdose. Toward this end, the crystal structure of an engineered murine-human chimeric Fab of GNC92H2 complexed with cocaine was determined at 2.3 A resolution. Structural analysis reveals a binding pocket with high shape and charge complementarity to the cocaine framework, which explains the specificity for cocaine, as opposed to the pharmacologically inactive cocaine metabolites. Importantly, the structure provides a foundation for mutagenesis to enhance the binding affinity for cocaine and potent cocaine derivatives, such as cocaethylene, and for additional humanization of the antibody.

Impact of ligand and protein desolvation on ligand binding to the S1 pocket of thrombin

In the present study, we investigate the impact of a tightly bound water molecule on ligand binding in the S1 pocket of thrombin. The S1 pocket contains a deeply buried deprotonated aspartate residue (Asp189) that is, due to its charged state, well hydrated in the uncomplexed state. We systematically studied the importance of this water molecule by evaluating a series of ligands that contains pyridine-type P1 side chains that could potentially alter the binding properties of this water molecule. All of the pyridine derivatives retain the original hydration state albeit sometimes with a slight perturbance. In order to prevent a direct H-bond formation with Asp189, and to create a permanent positive charge on the P1 side chain that is positioned adjacent to the Asp189 carboxylate anion, we methylated the pyridine nitrogen. This methylation resulted in displacement of water but was accompanied by a loss in binding affinity. Quantum chemical calculations of the ligand solvation free energy showed that the positively charged methylpyridinium derivatives suffer a large penalty of desolvation upon binding. Consequently, they have a substantially less favorable enthalpy of binding. In addition to the ligand desolvation penalty, the hydration shell around Asp189 has to be overcome, which is achieved in nearly all pyridinium derivatives. Only for the ortho derivative is a partial population of a water next to Asp189 found. Possibly, the gain of electrostatic interactions between the charged P1 side chain and Asp189 helps to compensate for the desolvation penalty. In all uncharged pyridine derivatives, the solvation shell remains next to Asp189, partly mediating interactions between ligand and protein. In the case of the para-pyridine derivative, a strongly disordered cluster of water sites is observed between ligand and Asp189.

A new functional domain of guanine nucleotide dissociation inhibitor (alpha-GDI) involved in Rab recycling

Guanine nucleotide dissociation inhibitor (GDI) is a 55-kDa protein that functions in vesicular membrane transport to recycle Rab GTPases. We have now determined the crystal structure of bovine alpha-GDI at ultra-high resolution (1.04 A). Refinement at this resolution highlighted a region with high mobility of its main-chain residues. This corresponded to a surface loop in the primarily alpha-helical domain II at the base of alpha-GDI containing the previously uncharacterized sequence-conserved region (SCR) 3A. Site-directed mutagenesis showed that this mobile loop plays a crucial role in binding of GDI to membranes and extraction of membrane-bound Rab. This domain, referred to as the mobile effector loop, in combination with Rab-binding residues found in the multi-sheet domain I at the apex of alpha-GDI may provide flexibility for recycling of diverse Rab GTPases. We propose that conserved residues in domains I and II synergize to form the functional face of GDI, and that domain II mediates a critical step in Rab recycling during vesicle fusion.

Using antibody catalysis to study the outcome of multiple evolutionary trials of a chemical task

Catalytic aldolase antibodies generated by immunization with two different, but structurally related, beta-diketone haptens were cloned and sequenced to study similarities and differences between independently evolved catalysts. Kinetic and sequence analysis coupled with mutagenesis, structural, and modeling studies reveal that the defining event in the evolution of these catalysts was a somatic mutation that placed a lysine residue in a deep, yet otherwise unrefined, hydrophobic pocket. We suggest that covalent chemistries may be as readily selected from the immune repertoire as the traditional noncovalent interactions that have formed the basis of immunochemistry until this time. Further, we believe that these experiments recapitulate the defining events in the evolution of nature's enzymes, particularly as they relate to chemical mechanism, catalytic promiscuity, and gene duplication.

Unilateral localized basaliomatosis: treatment with topical photodynamic therapy after application of 5-aminolevulinic acid

A 74-year-old woman presenting with multiple unilateral localized basal cell carcinomas present for 30 years on the left side of her body is reported. There was no history of arsenic ingestion or X-ray exposure. Typical signs of nevoid basal-cell carcinoma syndrome (Gorlin's syndrome) like jaw keratocysts, skeletal malformations, and small palmoplantar pits were missing. Although treatment with many therapeutic regimens was tried, there were still tumor recurrences. Photodynamic therapy was performed after topical application of 5-aminolevulinic acid. This treatment resulted in good tumor control with an optimal cosmetic result.

Different behavioral and eye movement patterns of dyslexic readers with and without attentional deficits during single word reading

Comorbidity of learning disabilities is a very common phenomenon which is intensively studied in genetics, neuropsychology, prevalence studies and causal deficit research. In studies on the behavioral manifestation of learning disabilities, however, comorbidity is often neglected. In the present study, we systematically examined the reading behavior of German-speaking children with dyslexia, of children with attentional problems, of children with comorbid dyslexia and attentional problems and of normally developing children by measuring their reading accuracy, naming latencies and eye movement patterns during single word reading. We manipulated word difficulty by contrasting (1) short vs. long words with (2) either low or high sublexical complexity (indexed by consonant cluster density). Children with dyslexia only (DYS) showed the expected reading fluency impairment of poor readers in regular orthographies but no accuracy problem. In contrast, comorbid children (DYS+AD) had significantly higher error rates than all other groups, but less of a problem with reading fluency than DYS. Concurrently recorded eye movement measures revealed that DYS made the highest number of fixations, but exhibited shorter mean single fixations than DYS+AD. Word length had the strongest effect on dyslexic children, whereas consonant cluster density affected all groups equally. Theoretical implications of these behavioral and eye movement patterns are discussed and the necessity for controlling for comorbid attentional deficits in children with reading deficits is highlighted.