A mimetic peptide of ACE2 protects against SARS-CoV-2 infection and decreases pulmonary inflammation related to COVID-19.

Since human angiotensin-converting enzyme 2 (ACE2) serves as a primary receptor for SARS-CoV-2, characterizing ACE2 regions that allow SARS-CoV-2 to enter human cells is essential for designing peptide-based antiviral blockers and elucidating the pathogenesis of the virus. We identified and synthesized a 25-mer mimetic peptide (encompassing positions 22-46 of the ACE2 alpha-helix α1) implicated in the S1 receptor-binding domain (RBD)-ACE2 interface. The mimetic (wild-type, WT) ACE2 peptide significantly inhibited SARS-CoV-2 infection of human pulmonary Calu-3 cells in vitro. In silico protein modeling predicted that residues F28, K31, F32, F40, and Y41 of the ACE2 alpha-helix α1 are critical for the original, Delta, and Omicron strains of SARS-CoV-2 to establish the Spike RBD-ACE2 interface. Substituting these residues with alanine (A) or aspartic acid (D) abrogated the antiviral protective effect of the peptides, indicating that these positions are critical for viral entry into pulmonary cells. WT ACE2 peptide, but not the A or D mutated peptides, exhibited significant interaction with the SARS-CoV-2 S1 RBD, as shown through molecular dynamics simulations. Through identifying the critical amino acid residues of the ACE2 alpha-helix α1, which is necessary for the Spike RBD-ACE2 interface and mobilized during the in vitro viral infection of cells, we demonstrated that the WT ACE2 peptide protects susceptible K18-hACE2 mice against in vivo SARS-CoV-2 infection and is effective for the treatment of COVID-19.

The AIRE G228W mutation disturbs the interaction of AIRE with its partner molecule SIRT1.

The autoimmune regulator (AIRE) protein functions as a tetramer, interacting with partner proteins to form the "AIRE complex," which relieves RNA Pol II stalling in the chromatin of medullary thymic epithelial cells (mTECs). AIRE is the primary mTEC transcriptional controller, promoting the expression of a large set of peripheral tissue antigen genes implicated in the negative selection of self-reactive thymocytes. Under normal conditions, the SIRT1 protein temporarily interacts with AIRE and deacetylates K residues of the AIRE SAND domain. Once the AIRE SAND domain is deacetylated, the binding with SIRT1 is undone, allowing the AIRE complex to proceed downstream with the RNA Pol II to the elongation phase of transcription. Considering that the in silico and in vitro binding of the AIRE SAND domain with SIRT1 provides a powerful model system for studying the dominant SAND G228W mutation mechanism, which causes the autoimmune polyglandular syndrome-1, we integrated computational molecular modeling, docking, dynamics between the whole SAND domain with SIRT1, and surface plasmon resonance using a peptide harboring the 211 to 230 residues of the SAND domain, to compare the structure and energetics of binding/release between AIRE G228 (wild-type) and W228 (mutant) SAND domain to SIRT1. We observed that the G228W mutation in the SAND domain negatively influences the AIRE-SIRT1 interaction. The disturbed interaction might cause a disruption in the binding of the AIRE SAND domain with the SIRT1 catalytic site, impairing the AIRE complex to proceed downstream with RNA Pol II.

Computer simulations of the refolding of sperm whale apomyoglobin from high-temperature denaturated state.

The refolding mechanism of apomyoglobin (apoMb) subsequent to high-temperature unfolding has been examined using computer simulations with atomic level detail. The folding of this protein has been extensively studied experimentally, providing a large database of folding parameters which can be probed using simulations. In the present study, 4-folding trajectories of apoMb were computed starting from coiled structures. A crystal structure of sperm whale myoglobin taken from the Protein Data Bank was used to construct the final native conformation by removal of the heme group followed by energy optimization. The initial unfolded conformations were obtained from high-temperature molecular dynamics simulations. Room-temperature refolding trajectories at neutral pH were obtained using the stochastic difference equation in length algorithm. The folding trajectories were compared with experimental results and two previous molecular dynamics studies at low pH. In contrast to the previous simulations, an extended intermediate with large helical content was not observed. In the present study, a structural collapse occurs without formation of helices or native contacts. Once the protein structure is more compact (radius of gyration<18 A) secondary and tertiary structures appear. These results suggest that apoMb follows a different folding pathway after high-temperature denaturation.

Social stress does not interact with paradoxical sleep deprivation-induced memory impairment.

Extensive evidence has linked both paradoxical sleep (PS) and stress to memory processing. The purpose of the present study was to examine the effect of social instability stress on memory and to verify whether this stress interferes with the amnesic effect of PS deprivation using the modified multiple platform method. In addition to the PS-deprived group (put onto narrow platforms inside the deprivation tanks) two control groups were used: one of them remained in its home-cages and the other was placed inside the deprivation tanks, onto a grid that contained large platforms on it. All groups were subdivided in socially stable and unstable conditions. Immediately after 96 h of sleep deprivation, the animals were trained in three different memory tasks: inhibitory avoidance, classical fear conditioning to a discrete stimulus and contextual fear conditioning. Twenty-four hours after training, the animals were tested in order to assess task acquisition. The results showed that social instability did not impair the performance of animals nor interacted with PS deprivation in any of the tasks. Grid control animals presented a selective impairment in the inhibitory avoidance task and contextual, but not in the classical, fear conditioning task, compared to cage control rats. This finding could be due to the stress to which grid control animals were exposed (humidity and luminosity) during the manipulation period. PS-deprived animals exhibited poorer performance than the other groups in all tasks. As they also showed an increased threshold to shock-induced vocalisation, but not to flinch response, it is not possible to completely rule out a decreased response to noxious stimulation as a contributing factor for the present results with PS deprivation.

Barrier Crossing in Dihydrofolate Reductasedoes not involve a rate-promoting vibration.

We have studied atomic motions during the chemical reaction catalyzed by the enzyme dihydrofolate reductase of Escherichia coli (EcDHFR), an important enzyme for nucleic acid synthesis. In our earlier work on the enzymes human lactate dehydrogenase and purine nucleoside phosphorylase, we had identified fast sub-ps motions that are part of the reaction coordinate. We employed Transition Path Sampling (TPS) and our recently developed reaction coordinate identification methodology to investigate if such fast motions couple to the reaction in DHFR on the barrier-crossing timescale. While we identified some protein motions near the barrier crossing event, these motions do not constitute a compressive promoting vibration, and do not appear as a clearly identifiable protein component in reaction.