Catalytic mechanism of Escherichia coli ribonuclease III: kinetic and inhibitor evidence for the involvement of two magnesium ions in RNA phosphodiester hydrolysis

Escherichia coli ribonuclease III (RNase III; EC 3.1.24) is a double-stranded(ds)-RNA-specific endonuclease with key roles in diverse RNA maturation and decay pathways. E.coli RNase III is a member of a structurally distinct superfamily that includes Dicer, a central enzyme in the mechanism of RNA interference. E.coli RNase III requires a divalent metal ion for activity, with Mg(2+) as the preferred species. However, neither the function(s) nor the number of metal ions involved in catalysis is known. To gain information on metal ion involvement in catalysis, the rate of cleavage of the model substrate R1.1 RNA was determined as a function of Mg(2+) concentration. Single-turnover conditions were applied, wherein phosphodiester cleavage was the rate-limiting event. The measured Hill coefficient (n(H)) is 2.0 ± 0.1, indicative of the involvement of two Mg(2+) ions in phosphodiester hydrolysis. It is also shown that 2-hydroxy-4H-isoquinoline-1,3-dione—an inhibitor of ribonucleases that employ two divalent metal ions in their catalytic sites—inhibits E.coli RNase III cleavage of R1.1 RNA. The IC(50) for the compound is 14 μM for the Mg(2+)-supported reaction, and 8 μM for the Mn(2+)-supported reaction. The compound exhibits noncompetitive inhibitory kinetics, indicating that it does not perturb substrate binding. Neither the O-methylated version of the compound nor the unsubstituted imide inhibit substrate cleavage, which is consistent with a specific interaction of the N-hydroxyimide with two closely positioned divalent metal ions. A preliminary model is presented for functional roles of two divalent metal ions in the RNase III catalytic mechanism

Preparation of 4 '-spirocyclobutyl nucleoside analogues as novel and versatile adenosine scaffolds

Despite the large variety of modified nucleosides that have been reported, the preparation of constrained 4 '-spirocyclic adenosine analogues has received very little attention. We discovered that the [2+2]-cycloaddition of dichloroketene on readily available 4 '-exo-methylene furanose sugars efficiently results in the diastereoselective formation of novel 4 '-spirocyclobutanones. The reaction mechanism was investigated via density functional theory (DFT) and found to proceed either via a non-synchronous or stepwise reaction sequence, controlled by the stereochemistry at the 3 '-position of the sugar substrate. The obtained dichlorocyclobutanones were converted into nucleoside analogues, providing access to a novel class of chiral 4 '-spirocyclobutyl adenosine mimetics in eight steps from commercially available sugars. Assessment of the biological activity of designed 4 '-spirocyclic adenosine analogues identified potent inhibitors for protein methyltransferase target PRMT5

Acute myocardial infarction after inactivated COVID-19 vaccination: a case report and literature review

A number of vaccines have been developed and deployed globally to restrain the spreading of the coronavirus disease 2019 (COVID-19). The adverse effect following vaccination is an important consideration. Acute myocardial infarction (AMI) is a kind of rare adverse event after COVID-19 vaccination. Herein, we present a case of an 83-year-old male who suffered cold sweat ten minutes after the first inactivated COVID-19 vaccination and AMI one day later. The emergency coronary angiography showed coronary thrombosis and underlying stenosis in his coronary artery. Type II Kounis syndrome might be a potential mechanism, which is manifested as coronary thrombosis secondary to allergic reactions in patients with underlying asymptomatic coronary heart disease. We also summarize the reported AMI cases post COVID-19 vaccination, as well as overview and discuss the proposed mechanisms of AMI after COVID-19 vaccination, thus providing insights for clinicians to be aware of the possibility of AMI following COVID-19 vaccination and potential underlying mechanisms

Incomplete Inhibition of Sphingosine 1-Phosphate Lyase Modulates Immune System Function yet Prevents Early Lethality and Non-Lymphoid Lesions

BACKGROUND: S1PL is an aldehyde-lyase that irreversibly cleaves sphingosine 1-phosphate (S1P) in the terminal step of sphingolipid catabolism. Because S1P modulates a wide range of physiological processes, its concentration must be tightly regulated within both intracellular and extracellular environments. METHODOLOGY: In order to better understand the function of S1PL in this regulatory pathway, we assessed the in vivo effects of different levels of S1PL activity using knockout (KO) and humanized mouse models. PRINCIPAL FINDINGS: Our analysis showed that all S1PL-deficient genetic models in this study displayed lymphopenia, with sequestration of mature T cells in the thymus and lymph nodes. In addition to the lymphoid phenotypes, S1PL KO mice (S1PL(-/-)) also developed myeloid cell hyperplasia and significant lesions in the lung, heart, urinary tract, and bone, and had a markedly reduced life span. The humanized knock-in mice harboring one allele (S1PL(H/-)) or two alleles (S1PL(H/H)) of human S1PL expressed less than 10 and 20% of normal S1PL activity, respectively. This partial restoration of S1PL activity was sufficient to fully protect both humanized mouse lines from the lethal non-lymphoid lesions that developed in S1PL(-/-) mice, but failed to restore normal T-cell development and trafficking. Detailed analysis of T-cell compartments indicated that complete absence of S1PL affected both maturation/development and egress of mature T cells from the thymus, whereas low level S1PL activity affected T-cell egress more than differentiation. SIGNIFICANCE: These findings demonstrate that lymphocyte trafficking is particularly sensitive to variations in S1PL activity and suggest that there is a window in which partial inhibition of S1PL could produce therapeutic levels of immunosuppression without causing clinically significant S1P-related lesions in non-lymphoid target organs

Catalytic mechanism of ribonuclease III: kinetic and inhibitor evidence for the involvement of two magnesium ions in RNA phosphodiester hydrolysis-2

<p><b>Copyright information:</b></p><p>Taken from "Catalytic mechanism of ribonuclease III: kinetic and inhibitor evidence for the involvement of two magnesium ions in RNA phosphodiester hydrolysis"</p><p>Nucleic Acids Research 2005;33(3):807-815.</p><p>Published online 7 Feb 2005</p><p>PMCID:PMC549391.</p><p>© The Author 2005. Published by Oxford University Press. All rights reserved</p

Catalytic mechanism of ribonuclease III: kinetic and inhibitor evidence for the involvement of two magnesium ions in RNA phosphodiester hydrolysis-1

<p><b>Copyright information:</b></p><p>Taken from "Catalytic mechanism of ribonuclease III: kinetic and inhibitor evidence for the involvement of two magnesium ions in RNA phosphodiester hydrolysis"</p><p>Nucleic Acids Research 2005;33(3):807-815.</p><p>Published online 7 Feb 2005</p><p>PMCID:PMC549391.</p><p>© The Author 2005. Published by Oxford University Press. All rights reserved</p