Inactivation of Trypanosoma cruzi Trypomastigote Forms in Blood Components with a Psoralen and Ultraviolet A Light

Inactivation of the blood-borne parasite Trypanosoma cruzi by UVA and 4'-aminomethyl-4,5',8-trimethylpsor-alen (AMT) was studied in the blood components fresh frozen plasma (FFP) and platelet concentrate (PC). The AMT was utilized at a concentration of 50 μg/mL and the inactivation procedure included the flavonoid rutin (at 0.35 mM), a quencher of type I and type II photo-reactants, which we have previously found to maintain platelet integrity during this treatment regimen. Within both FFP and PC, complete inactivation of the infective form of T. cruzi , the trypomastigote, was achieved at a UVA (320–400 nm radiation) fluence of 4.2 J/cm². We note that while the infectivity of the parasite is eliminated at 4.2 J/cm^Z the trypomastigote motility continues for at least 16 h post-treatment and is inhibited only after much higher light doses. Isolation of total DNA from the parasite cells after treatment in the presence of ³H-AMT indicated that at the lethal UVA fluence about 0.5 AMT adducts per kilobase pairs occurred. These results suggest that this psoralen plus UVA methodology, which shows promise in enhancing the viral safety of PC, may in addition eliminate bloodborne T. cruzi , the causative agent of Chagas disease.     

The self‐assembling zwitterionic form of L‐phenylalanine at neutral pH

The title zwitterion (2S)‐2‐azaniumyl‐1‐hydroxy‐3‐phenylpropan‐1‐olate, C₉H₁₁NO₂, also known as L‐phenylalanine, was characterized using synchrotron X‐rays. It crystallized in the monoclinic space group P2₁ with four molecules in the asymmetric unit. The 0.62 Å resolution structure is assumed to be closely related to the fibrillar form of phenylalanine, as observed by electron microscopy and electron diffraction. The structure exists in a zwitterionic form in which π–π stacking and hydrogen‐bonding interactions are believed to form the basis of the self‐assembling properties.     

Switchable Cucurbituril–Bipyridine Beacons

4‐Aminobipyridine derivatives form strong inclusion complexes with cucurbit[6]uril, exhibiting remarkably large enhancements in fluorescence intensity and quantum yields. The remarkable complexation‐induced pK_a shift (ΔpK_a=3.3) highlights the strong charge–dipole interaction upon binding. The reversible binding phenomenon can be used for the design of switchable beacons that can be incorporated into cascades of binding networks. This concept is demonstrated herein by three different applications: 1) a switchable fluorescent beacon for chemical sensing of transition metals and other ligands; 2) direct measurement of binding constants between cucurbit[6]uril and various nonfluorescent guest molecules; and 3) quantitative monitoring of biocatalytic reactions and determination of their kinetic parameters. The latter application is illustrated by the hydrolysis of an amide catalyzed by penicillin G acylase and by the elimination reaction of a β‐cabamoyloxy ketone catalyzed by aldolase antibody 38C2.     

Direct observation of the release of phenylalanine from diphenylalanine nanotubes

The core recognition motif of the amyloidogenic beta-amyloid polypeptide is a dipeptide of phenylalanine. This dipeptide readily self-assembles to form discrete, hollow nanotubes with high persistence lengths. The simplicity of the nanotube formation, combined with ideal physical properties, make these nanotubes highly desirable for a range of applications in bionanotechnology. To fully realize the potential of such structures, it is first necessary to gain a comprehensive understanding of their chemical and physical properties. Previously, the thermal stability of these nanotubes has been investigated by electron microscopy. Here, we further our understanding of the structural stability of the nanotubes upon dry-heating using the atomic force microscope (AFM), and for the first time identify their degradation product utilizing time-of-flight secondary-ion mass spectrometry. We show that the nanotubes are stable at temperatures up to 100 degrees C, but on heating to higher temperatures begin to lose their structural integrity with an apparent collapse in tubular structure. With further increases in temperature up to and above 150 degrees C, there is a degradation of the structure of the nanotubes through the release of phenylalanine building blocks. The breakdown of structure is observed in samples that are either imaged at elevated temperatures or imaged following cooling, suggesting that once phenylalanine is lost from the nanotubes they are susceptible to mechanical deformation by the imaging AFM probe. This temperature-induced plasticity may provide novel properties for these peptide nanotubes, including possible applications as scaffolds and drug delivery devices.     

Understanding the enzymatic activity of 4-oxalocrotonate tautomerase and its mutant analogues: a computational study

The effect of replacing arginine residues (Arg) with citrulline residues (Cit) in the binding site of 4-oxalocrotonate tautomerase (4-OT) was investigated with force field molecular dynamics and hybrid quantum mechanics/molecular mechanics studies. It is found that the Arg61Cit mutation has only minor effects on the k(cat) and K(M) values determined experimentally because of the flexibility of this residue. The decrease in k(cat) and increase in K(M) for the Arg11Cit and Arg39Cit mutations are due to the disruption of the binding site, which arises from repulsive interactions with neighboring residues. The results of this investigation shed new light on the effects of mutations in the binding site of 4-OT and consequently on how the enzyme binds the active substrate.     

The Metabolostasis Network and the Cellular Depository of Aggregation-Prone Metabolites

The vital role of metabolites across all branches of life and their involvement in various disorders have been investigated for decades. Many metabolites are poorly soluble in water or in physiological buffers and tend to form supramolecular aggregates. On the other hand, in the cell, they should be preserved in a pool and be readily available for the execution of biochemical functions. We thus propose that a quality-control network, termed “metabolostasis”, has evolved to regulate the storage and retrieval of aggregation-prone metabolites. Such a system should control metabolite concentration, subcellular localization, supramolecular arrangement, and interaction in dynamic environments, thus enabling normal cellular physiology, healthy development, and preventing disease onset. The paradigm-shifting concept of metabolostasis calls for a reevaluation of the traditional view of metabolite storage and dynamics in physiology and pathology and proposes unprecedented directions for therapeutic targets under conditions where metabolostasis is imbalanced.     

Tailored Host–Guest Lipidic Cubic Phases: A Protocell Model Exhibiting Nucleic Acid Recognition

A classical conundrum in origin‐of‐life studies relates to the nature of the first chemical system: was it a carrier of genetic information or a facilitator of cellular compartmentalization? Here we present a system composed of tailor‐made nucleolipids and hydrated monoolein, which assemble at ambient temperatures to form host–guest lipidic cubic phase (LCP) materials that are stable in bulk water and can perform both functions. As such, they may represent a molecular model for a protocell in origin‐of‐life studies. Nucleolipids within the lipidic material sequester and bind selectively complementary oligonucleotide sequences from solution by virtue of base‐pairing; noncomplementary sequences diffuse freely between the LCP material and the bulk aqueous environment. Sequence specific enrichment of nucleic acids within the LCP material demonstrates an effective mechanism for selection of genetic material in these cell‐mimetic systems.