LTP Induction Boosts Glutamate Spillover by Driving Withdrawal of Perisynaptic Astroglia

Extrasynaptic actions of glutamate are limited by high-affinity transporters expressed by perisynaptic astroglial processes (PAPs): this helps maintain point-to-point transmission in excitatory circuits. Memory formation in the brain is associated with synaptic remodeling, but how this affects PAPs and therefore extrasynaptic glutamate actions is poorly understood. Here, we used advanced imaging methods, in situ and in vivo, to find that a classical synaptic memory mechanism, long-term potentiation (LTP), triggers withdrawal of PAPs from potentiated synapses. Optical glutamate sensors combined with patch-clamp and 3D molecular localization reveal that LTP induction thus prompts spatial retreat of astroglial glutamate transporters, boosting glutamate spillover and NMDA-receptor-mediated inter-synaptic cross-talk. The LTP-triggered PAP withdrawal involves NKCC1 transporters and the actin-controlling protein cofilin but does not depend on major Ca2+-dependent cascades in astrocytes. We have therefore uncovered a mechanism by which a memory trace at one synapse could alter signal handling by multiple neighboring connections.

Ancestral Protein Reconstruction and Circular Permutation for Improving the Stability and Dynamic Range of FRET Sensors

Small molecule biosensors based on Förster resonance energy transfer (FRET) enable small molecule signaling to be monitored with high spatial and temporal resolution in complex cellular environments. FRET sensors can be constructed by fusing a pair of fluorescent proteins to a suitable recognition domain, such as a member of the solute-binding protein (SBP) superfamily. However, naturally occurring SBPs may be unsuitable for incorporation into FRET sensors due to their low thermostability, which may preclude imaging under physiological conditions, or because the positions of their N- and C-termini may be suboptimal for fusion of fluorescent proteins, which may limit the dynamic range of the resulting sensors. Here, we show how these problems can be overcome using ancestral protein reconstruction and circular permutation. Ancestral protein reconstruction, used as a protein engineering strategy, leverages phylogenetic information to improve the thermostability of proteins, while circular permutation enables the termini of an SBP to be repositioned to maximize the dynamic range of the resulting FRET sensor. We also provide a protocol for cloning the engineered SBPs into FRET sensor constructs using Golden Gate assembly and discuss considerations for in situ characterization of the FRET sensors.

Correction: Antimicrobial stewardship in patients recently transferred to a ward from the ICU

This paper is a corrigendum to the previously published paper: "Antimicrobial stewardship in patients recently transferred to a ward from the ICU" [Rev Esp Quimioter. 2014 Mar;27(1):46-50.] This corrigendum was prepared in order to correct some erroneous comments included in the discussion section. First, it should be pointed out that there could have been several suitable options for treating many infections and that, therefore, the word "inadequate" was not the most appropriate in this situation. In addition, some comments about the interpretation of microbiological results made by ICU physicians have been removed from the first article because this variable was not included in the study. Finally, another change made to the discussion was to clarify the ICU physicians' alleged low level of compliance with advice given by infectious disease specialists. This has been suggested in previous studies it cannot be substantiated when analyzing the results of the study.

PURPOSE

Inappropriate use of antibiotics is an important health problem that is related to increasing bacterial resistance. Despite its relevance, many health institutions assign very limited resources to improving prescribing practices. An antimicrobial stewardship programme (APS) centred on patients discharged from the ICU could efficiently undertake this task.

METHODS

During this six month study the main activity was performing a programmed review of antimicrobial prescriptions in patients transferred to the ward from the ICU. In the case of amendable antimicrobial treatment, a recommendation was included in the medical record.

RESULTS

A total of 437 antimicrobial prescriptions for 286 patients were revised during a six month period and a total of 271 prescriptions (62%) in 183 patients were considered to be amendable. In most of these cases, treatment could have been reduced taking into consideration each patient's clinical improvement and their location in a hospital area with a lower risk of infection due to resistant bacteria. The most common advice was antimicrobial withdrawal (64%), antimicrobial change (20%) and switching to oral route (12%). Proposed recommendations were addressed in 212 cases (78%). There was no significant difference in adherence with respect to the type of recommendation (p=0.417). There was a 5% lower use of antibiotics during the year the study was conducted compared to the previous one.

CONCLUSIONS

ASPs centred on patients discharged from the ICU may be an efficient strategy to ameliorate antimicrobial use in hospitals.

Single-molecule paleoenzymology probes the chemistry of resurrected enzymes

A journey back in time is possible at the molecular level by reconstructing proteins from extinct organisms. Here we report the reconstruction, based on sequence predicted by phylogenetic analysis, of seven Precambrian thioredoxin enzymes (Trx), dating back between ~1.4 and ~4 billion years (Gyr). The reconstructed enzymes are up to 32° C more stable than modern enzymes and the oldest show significantly higher activity than extant ones at pH 5. We probed their mechanisms of reduction using single-molecule force spectroscopy. From the force-dependency of the rate of reduction of an engineered substrate, we conclude that ancient Trxs utilize chemical mechanisms of reduction similar to those of modern enzymes. While Trx enzymes have maintained their reductase chemistry unchanged, they have adapted over a 4 Gyr time span to the changes in temperature and ocean acidity that characterize the evolution of the global environment from ancient to modern Earth.

Diversity of chemical mechanisms in thioredoxin catalysis revealed by single-molecule force spectroscopy

Thioredoxins (Trxs) are oxidoreductase enzymes, present in all organisms, that catalyze the reduction of disulfide bonds in proteins. By applying a calibrated force to a substrate disulfide, the chemical mechanisms of Trx catalysis can be examined in detail at the single-molecule level. Here we use single-molecule force-clamp spectroscopy to explore the chemical evolution of Trx catalysis by probing the chemistry of eight different Trx enzymes. All Trxs show a characteristic Michaelis-Menten mechanism that is detected when the disulfide bond is stretched at low forces, but at high forces, two different chemical behaviors distinguish bacterial-origin from eukaryotic-origin Trxs. Eukaryotic-origin Trxs reduce disulfide bonds through a single-electron transfer reaction (SET), whereas bacterial-origin Trxs show both nucleophilic substitution (S(N)2) and SET reactions. A computational analysis of Trx structures identifies the evolution of the binding groove as an important factor controlling the chemistry of Trx catalysis.