Technical Data of Heterologous Expression and Purification of SARS-CoV-2 Proteases Using Escherichia coli System

The SARS-CoV-2 coronavirus expresses two essential proteases: firstly, the 3Chymotrypsin-like protease (3CLpro) or main protease (Mpro), and secondly, the papain-like protease (PLpro), both of which are considered as viable drug targets for the inhibition of viral replication. In order to perform drug discovery assays for SARS-CoV-2, it is imperative that efficient methods are established for the production and purification of 3CLpro and PLpro of SARS-CoV-2, designated as 3CLpro-CoV2 and PLpro-CoV2, respectively. This article expands the data collected in the attempts to express SARS-CoV-2 proteases under different conditions and purify them under single-step chromatography. Data showed that the use of E. coli BL21(DE3) strain was sufficient to express 3CLpro-CoV2 in a fully soluble form. Nevertheless, the single affinity chromatography step was only applicable for 3CLpro-CoV2 expressed at 18 °C, with a yield and purification fold of 92% and 49, respectively. Meanwhile, PLpro-CoV2 was successfully expressed in a fully soluble form in either BL21(DE3) or BL21-CodonPlus(DE3) strains. In contrast, the single affinity chromatography step was only applicable for PLpro-CoV2 expressed using E. coli BL21-CodonPlus(DE3) at 18 or 37 °C, with a yield and purification fold of 86% (18 °C) or 83.36% (37 °C) and 112 (18 °C) or 71 (37 °C), respectively. The findings provide a guide for optimizing the production of SARS-CoV-2 proteases of E. coli host cells.

Characterization of NADP-dependent L-arginine dehydrogenase as a novel amino acid dehydrogenase and its application to an L-arginine assay

Purpose: The primary aim of this study was the purification and characterization of an NADP-dependent L arginine dehydrogenase (L-ArgDH, EC 1.4.1.25) as a novel amino acid dehydrogenase from Pseudomonas veronii. We then applied the enzyme to an L-arginine assay. Methods: An L-ArgDH gene from P. veronii JCM11942 was amplified by PCR using primers based on the N and C-terminal sequences inferred from a putative L-ArgDH gene (PverR02_12350) found in the P. veronii genome. The L-ArgDH activity of the product expressed in Escherichia coli was confirmed, after which the enzyme was purified, characterized, and applied to an L-Arg microassay. Results: The P. veroniiJCM11942 gene was expressed in E. coli, and the gene product exhibited strong NADP dependent L-ArgDH activity. The crude enzyme was unstable but was stabilized by the presence of 10% glycerol under neutral pH conditions. The enzyme was purified to homogeneity through a single Ni-chelate affinity chromatography step and consisted of a homodimeric protein with a molecular mass of about 65 kDa. The enzyme selectively catalyzed L-arginine oxidation in the presence of NADP, with maximal activity at pH 9.5. The apparent Km values for L-arginine and NADP were 2.5 and 0.21 mM, respectively. A simple colorimetric microassay for L-arginine was achieved using the enzyme. Conclusions: The L-ArgDH gene from P. veronii JCM 11942 was successively expressed in E. coli. The product exhibited NADP-dependent L-ArgDH dehydrogenase activity, and the enzyme was purified and characterized as a novel amino acid dehydrogenase. Furthermore, a simple colorimetric assay for L-arginine using L-ArgDH was achieved. Conflict of interest: The authors declare that they have no competing interests.

Antigen production and development of an indirect ELISA based on the nucleocapsid protein to detect human SARS-CoV-2 seroconversion

Serological assays are important tools to identify previous exposure to SARS-CoV-2, helping to track COVID-19 cases and determine the level of humoral response to SARS-CoV-2 infections and/or immunization to future vaccines. Here the SARS-CoV-2 nucleocapsid protein was expressed in Escherichia coli and purified to homogeneity and high yield using a single chromatography step. The purified SARS-CoV-2 nucleocapsid protein was used to develop an indirect enzyme-linked immunosorbent assay for the identification of human SARS-CoV-2 seroconverts. The assay sensitivity and specificity were determined analyzing sera from 140 PCR-confirmed COVID-19 cases and 210 pre-pandemic controls. The assay operated with 90% sensitivity and 98% specificity; identical accuracies were obtained in head-to-head comparison with a commercial ELISA kit. Antigen coated plates were stable for up to 3 months at 4°C). The ELISA method described is ready to mass production and will be an additional toll to track COVID-19 cases.

Purification of recombinant SARS-CoV-2 spike, its receptor binding domain, and CR3022 mAb for serological assay

ABSTRACTSerology testing for COVID-19 is highly attractive because of the relatively short diagnosis time and the ability to test for an active immune response against the SARS-CoV-2. In many types of serology tests, the sensitivity and the specificity are directly influenced by the quality of the antigens manufactured. Protein purification of these recombinantly expressed viral antigens [e.g., spike and its receptor binding domain (RBD)] is an important step in the manufacturing process. Simple and high-capacity protein purification schemes for spike, RBD, and CR3022 mAb, recombinantly expressed in CHO and HEK293 cells, are reported in this article. The schemes consist of an affinity chromatography step and a desalting step. Purified proteins were validated in ELISA-based serological tests. Interestingly, extracellular matrix proteins [most notably heparan sulfate proteoglycan (HSPG)] were co-purified from spike-expressing CHO culture with a long cultivation time. HSPG-spike interaction could play a functional role in the pathology and the pathogenesis of SARS-CoV-2 and other coronaviruses.

A Novel, Multiple-Antigen Pneumococcal Vaccine Protects against LethalStreptococcus pneumoniaeChallenge

ABSTRACTCurrent vaccination againstStreptococcus pneumoniaeuses vaccines based on capsular polysaccharides from selected serotypes and has led to nonvaccine serotype replacement disease. We have investigated an alternative serotype-independent approach, using multiple-antigen vaccines (MAV) prepared fromS. pneumoniaeTIGR4 lysates enriched for surface proteins by a chromatography step after culture under conditions that induce expression of heat shock proteins (Hsp; thought to be immune adjuvants). Proteomics and immunoblot analyses demonstrated that, compared to standard bacterial lysates, MAV was enriched with Hsps and contained several recognized protective protein antigens, including pneumococcal surface protein A (PspA) and pneumolysin (Ply). Vaccination of rodents with MAV induced robust antibody responses to multiple serotypes, including nonpneumococcal conjugate vaccine serotypes. Homologous and heterologous strains ofS. pneumoniaewere opsonized after incubation in sera from vaccinated rodents. In mouse models, active vaccination with MAV significantly protected against pneumonia, while passive transfer of rabbit serum from MAV-vaccinated rabbits significantly protected against sepsis caused by both homologous and heterologousS. pneumoniaestrains. Direct comparison of MAV preparations made with or without the heat shock step showed no clear differences in protein antigen content and antigenicity, suggesting that the chromatography step rather than Hsp induction improved MAV antigenicity. Overall, these data suggest that the MAV approach may provide serotype-independent protection againstS. pneumoniae.

Modified method for qualitative thyroestatic substances determination in muscle tissue and urine of food producing animals and the application of Planar Thin Layer Chromatography 2D and 4x4D horizontal development.

Substances with thyreostatic action, also known as anti-hormones [AHs], are extracted by methanol in the presence of an internal standard. Percolation of the methanol extract through a mercurated adsorption mini-column allows a selective and reproducible extraction of the AHs by creating a specific complex with Hg ions. After elution of the Ahs with an acidic sodium chloride solution, the pH of the eluate is adjusted with buffer to 8,0 and allowed to react with NBDCl, a reagent which reacts only with thiols and amines. After reaction, the AH-NBD complexes formed are extracted in acid medium using TBME and after it has been dried down and reconstituted with TBME to the required volume, the ether fraction is spotted on to a HPTLC plate for horizontal development using sophisticated instrumentation. A cysteine water solution reacts with the AH-NBD complexes which are not fluorescent and they are converted into cystein-NBD complexes which are strongly fluorescent at 366 nm. This method, based on Verbeke R, de Brabander HF, 1984 method, has been modified in some steps concerning the mini-column preparation, the elution, the buffer replacement and chromatography step. The limit of detection no the plate, has been determined to be lower than lng by direct UV observation at 366nm, while the lower limit of detection achieved in the sample was 25 μg/kg.

20α- and 20β-dihydrocortisone may interfere in LC-MS/MS determination of cortisol in saliva and urine

Background LC-MS/MS methods offer high selectivity in cortisol determinations. However, endogenous steroid metabolites may still interfere and compromise the results, for example in the diagnosis of Cushing’s syndrome. Erroneously elevated cortisol may, in particular, be misleading at the low concentrations found in salivary samples obtained at late night and after dexamethasone suppression. Methods Interferences in our LC-MS/MS method used for determination of cortisol in saliva and urine were identified by comparing their retention times and mass spectra with those of pure candidate substances. The chromatographic conditions used in our LC-MS/MS method, including column and mobile phase gradient, were varied in order to separate the target compound from the interferences. Results Two interferences, which were co-eluting or eluting close to cortisol in our original method, were successfully separated from cortisol by adjustment of the chromatographic conditions. These interferences were found in both urine and saliva and were identified as the two endogenous cortisol isomers 20α- and 20β-dihydrocortisone. The isomers share molecular mass and mass spectrometric fragmentation pattern with cortisol using electrospray ionization in the positive-ion mode. Both give rise to the transitions m/z 363.1>121.1, 363.1>115.1 and 363.1>97.1. In our original LC-MS/MS setup, the 20β-dihydrocortisone co-eluted with cortisol in the chromatography step resulting in false high determinations. Conclusions Cortisol determination by LC-MS/MS may suffer from erroneously elevated results unless 20α- and 20β-dihydrocortisone are chromatographically separated from cortisol.