Nanomedicine: Action of Metal Nanoparticles on Neuronal Nitric Oxide Synthase—Fluorimetric Analysis on the Mechanism for Fibrillogenesis

The incubation of neuronal nitric oxide synthase with the five amyloid peptide fragments [Aβ_17–21; Aβ_25–29; Aβ_29–33; Aβ_33–37; Aβ_25–37] catalyzed the formation of fibrils. The role of neuronal isomer (nNOS) involved the entrapment of free monomers and seed aggregates to initiate the events of nucleation and elongation, critical for the formation of fibrils. It was evident that the hydrophobic nature of Aβ_17–21, the three glycine zipper peptides [Aβ_25–29; Aβ_29–33; Aβ_33–37] and Aβ_25–37 was a trigger in the formation of fibrils and was a force critical in the association of the peptides with the enzyme. Gold and silver nanoparticles (average 4.0 nm) inhibited fibril formation when added to the induced fibrils from nNOS-Aβ incubation. The addition of nNOS and/or Aβ to co-incubated solutions of nanoparticle-Aβ or nanoparticle-nNOS respectively did not prevent fibril formation but reversed it. Three mechanisms for this reversal were proposed: (1) depletion of free Aβ monomer in solution and blocking potential aggregation sites on the nNOS molecule due to large surface area of the nanoparticle (2) hydrophobic interaction between the Aβ peptide and nanoparticle (3) disruption of binary adducts between Aβ-peptides and nNOS by nanoparticles.     

Induced synthesis of formyltetrahydrofolate synthetase in Micrococcus aerogenes

Summary The levels of formyltetrahydrofolate synthetase and cyclohydrolase in M. aerogenes were enhanced 3-to 10-fold by growth in media containing formate of histidine. This induced synthesis was decreased by the simultaneous addition of ribosides or ribotides. Histidine, but not formate, also induced the synthesis of formimino transferase and/or cyclodeaminase. The specific activities of N¹⁰-formyltetrahydrofolate deacylase, serine hydroxymethylase and N⁵, N¹⁰-methylenetetrahydrofolate dehydrogenase were not affected by formate or histidine. These observations have been discussed with respect to the known mechanisms of regulation of tetrahydrofolate linked enzymes.Dedicated to Prof. C. B. van Niel on the occasion of his 70th birthday.Recipient of Research Career Award GM-K6-422.     

Public Health Investigation of Two Outbreaks of Shiga Toxin-Producing Escherichia coli O157 Associated with Consumption of Watercress

An increase in the number of cases of Shiga toxin-producing Escherichia coli (STEC) O157 phage type 2 (PT2) in England in September 2013 was epidemiologically linked to watercress consumption. Whole-genome sequencing (WGS) identified a phylogenetically related cluster of 22 cases (outbreak 1). The isolates comprising this cluster were not closely related to any other United Kingdom strain in the Public Health England WGS database, suggesting a possible imported source. A second outbreak of STEC O157 PT2 (outbreak 2) was identified epidemiologically following the detection of outbreak 1. Isolates associated with outbreak 2 were phylogenetically distinct from those in outbreak 1. Epidemiologically unrelated isolates on the same branch as the outbreak 2 cluster included those from human cases in England with domestically acquired infection and United Kingdom domestic cattle. Environmental sampling using PCR resulted in the isolation of STEC O157 PT2 from irrigation water at one implicated watercress farm, and WGS showed this isolate belonged to the same phylogenetic cluster as outbreak 2 isolates. Cattle were in close proximity to the watercress bed and were potentially the source of the second outbreak. Transfer of STEC from the field to the watercress bed may have occurred through wildlife entering the watercress farm or via runoff water. During this complex outbreak investigation, epidemiological studies, comprehensive testing of environmental samples, and the use of novel molecular methods proved invaluable in demonstrating that two simultaneous outbreaks of STEC O157 PT2 were both linked to the consumption of watercress but were associated with different sources of contamination.