A molecular sensor determines the ubiquitin substrate specificity of SARS-CoV-2 papain-like protease

The SARS-CoV-2 papain-like protease (PLpro) is a target for antiviral drug development. It is essential for processing viral polyproteins for replication and functions in host immune evasion by cleaving ubiquitin (Ub) and ubiquitin-like protein (Ubl) conjugates. While highly conserved, SARS-CoV-2 and SARS-CoV PLpro have contrasting Ub/Ubl substrate preferences. Using a combination of structural analyses and functional assays, we identify a molecular sensor within the S1 Ub-binding site of PLpro that serves as a key determinant of substrate specificity. Variations within the S1 sensor specifically alter cleavage of Ub substrates but not of the Ubl interferon-stimulated gene 15 protein (ISG15). Significantly, a variant of concern associated with immune evasion carries a mutation in the S1 sensor that enhances PLpro activity on Ub substrates. Collectively, our data identify the S1 sensor region as a potential hotspot of variability that could alter host antiviral immune responses to newly emerging SARS-CoV-2 lineages.

The auto-generated fragment of the Usp1 deubiquitylase is a physiological substrate of the N-end rule pathway

Deamidation of N-terminal Gln by the Ntaq1 Nt(Q)-amidase is a part of the Arg/N-end rule pathway, a ubiquitin-dependent proteolytic system. Here we identify Gln-Usp1(Ct), the C-terminal fragment of the autocleaved Usp1 deubiquitylase, as the first physiological Arg/N-end rule substrate that is targeted for degradation through deamidation of N-terminal Gln. Usp1 regulates genomic stability, in part through the deubiquitylation of monoubiquitylated PCNA, a DNA polymerase processivity factor. The autocleaved Usp1 remains a deubiquitylase because its fragments remain associated with Uaf1, an enhancer of Usp1 activity, until the Gln-Usp1(Ct) fragment is selectively destroyed by the Arg/N-end rule pathway. We also show that metabolic stabilization of Gln-Usp1(Ct) results in a decreased monoubiquitylation of PCNA and in a hypersensitivity of cells to ultraviolet irradiation. Thus, in addition to its other functions in DNA repair and chromosome segregation, the Arg/N-end rule pathway regulates genomic stability through the degradation-mediated control of the autocleaved Usp1 deubiquitylase.

Influence of acetylsalicylic acid on acute circulatory effects of the beta-blocking agents pindolol and propranolol in humans

In ten hospitalized, hypertensive male patients (WHO stage I or II) an acetylsalicylic acid (ASA) pretreatment (p.o. 5.0 g/24 h) prevented the acute blood pressure (BP) lowering effect of pindolol (1 mg i.v.) as compared with a placebo pretreatment. Similarly in six other hospitalized male patients (four normotensive, two slightly hypertensive) a single dose of ASA (1.0 or 1.5 g orally), which alone tended to raise the BP, reduced the decrease in systolic BP and led to an increase in diastolic BP following propranolol (5 mg i.v.). The ASA pretreatment did not affect the decrease in heart rate and cardiac contractility (measured by systolic time intervals) after the application of pindolol and propranolol, respectively. In conformity with data in the literature, the results suggest a possible connection between endogenous prostaglandins and the hypotensive, but not negative chronotropic and inotropic activity of the beta-blocking agents investigated.

Comparative study of the cardiac and peripheral vascular effects of strophantin K and lanatoside C in coronary heart disease

The effects of intravenous strophanthin K (0.125 and 0.25 MG) and lanatoside C (0.4, 0.8 and 1.6 mg) on systolic time intervals (STI) and impedance plethysmographic (IP)P values were studied in ten patients with compensated coronary heart disease. The heart rate decreased significantly during a two-hour study in the lying position after both glycosides and placebo; the systemic blood pressure remained unchanged. Electromechanical systole (QS2), left ventricular ejection time (LVET) and preejection period (PEP), corrected for heart rate (QS2I, LVETI, PEPI), showed no change after placebo. The glycosides caused no change in LVETI. QS2I was significantly shortened only after lanatoside C 1.6 mg. PEPI and ICT were significantly shortened by both doses of strophanthin K and lanatoside C; the effects were dose-related. Taking into consideration the effects of cardiac glycosides on STI, use of the index ICT/QS1, the quotient of isovolumic contraction time and electro-mechanical delay, is proposed, because it showed quite sensitively the increase in myocardial contractility after digitalis. The effect of strophanthin K could be detected 10 minutes, and that of lanatoside C 30-40 minutes, after injection. The amplitude of the IP curve and the relative pulse volume showed positive and negative changes without any trend after administration of placebo or glycoside. The data suggests that the usual therapeutic doses of these cardiac glycosides do not cause significant changes in the peripheral circulation in patients with compensated coronary heart disease, but their action on STI is quite marked, showing a positive inotropic effect.