Recombinant Expression and Biophysical Characterization of a Druggable Schistosoma mansoni Universal Stress G4LZI3 Protein

Purpose: Universal stress protein from S. mansoni, designated as G4LZI3, was previously hypothesised as a druggable target and vaccine candidate for human schistosomiasis. The purpose of this study is to characterize a purified recombinant G4LZI3 preliminarily for subsequent structural characterisation, which will provide baseline structural data for future functional studies for the discovery, design and development of new schistosomal drugs for the treatment, control and elimination of schistosomiasis. Methods: Restriction digest analysis of a GenScript-synthesised codon-optimised G4LZI3 gene construct was carried out to ascertain its integrity and size. Thereafter, the pQE30-G4LZI3 construct was transformed into an M15 bacterial expression host. Transformed cells were induced with isopropyl β-D-thiogalactoside for recombinant protein expression of an appreciable amount of pQE30-G4LZI3, which was subsequently purified with fast protein liquid chromatography and a size exclusion chromatographic purification scheme. Preliminary biophysical characterisation of the 6X His-tagged G4LZI3 was done to determine its secondary structure characteristics and protein stability. Results: A molecular weight protein of 20.3 kDa was confirmed subsequent to restriction digest analysis, while heterologous protein expression yielded a highly soluble and considerable amount of histidine-tagged G4LZI3 protein, which was successfully purified to homogeneity. Biophysical characterisation indicated that the protein was well folded, heat-stable, had the functional groups and secondary structure composition required and was thus amenable to further structural characterisation and determination. Conclusion: Biophysical characterisation of purified G4LZI3 showed that further structural studies can be embarked upon on the use of G4LZI3 as a druggable target and possibly a vaccine target against schistosomiasis via vaccinomics.

A single-molecule counting approach for convenient and ultrasensitive measurement of restriction digest efficiencies

Restriction endonucleases play a central role in the microbial immune system against viruses and are widely used in DNA specific cleavage, which is called restriction digestion, for genetic engineering. Herein, we applied digital cell-free protein synthesis as an easy-to-use orthogonal readout means to assess the restriction digest efficiency, a new application of digital bioassays. The digital counting principle enabled an unprecedentedly sensitive trace analysis of undigested DNA at the single-molecule level in a PCR-free manner. Our approach can quantify the template DNA of much lower concentrations that cannot be detected by ensemble-based methods such as gold-standard DNA electrophoresis techniques. The sensitive and quantitative measurements revealed a considerable variation in the digest efficiency among restriction endonucleases, from less than 70% to more than 99%. Intriguingly, none of them showed truly complete digestion within reasonably long periods of reaction time. The same rationale was extended to a multiplexed assay and applicable to any DNA-degrading or genome-editing enzymes. The enzyme kinetic parameters and the flanking sequence-dependent digest efficiency can also be interrogated with the proposed digital counting method. The absolute number of residual intact DNA molecules per microliter was concluded to be at least 107, drawing attention to the residual issue of genetic materials associated with the interpretation of nucleases’ behaviors and functions in daily genetic engineering experiments.

The changing epidemiology of genital ulcer disease in South Africa: has donovanosis been eliminated?

ObjectivesWe used an in-house molecular assay for the detection of Klebsiella granulomatis in ulcer specimens collected over a 12-year surveillance period in order to determine whether a diagnosis of donovanosis could be ascribed to genital ulcer disease (GUD) of unknown aetiology in our setting.MethodsBetween 2007 and 2018, a total of 974 genital ulcer specimens with no previously identified sexually transmitted (STI) pathogens were selected from STI aetiological surveys conducted in all nine provinces of South Africa. Giemsa-stained ulcer smears from the same participants had previously been routinely analysed for the presence of typical Donovan bodies within large mononuclear cells. A Klebsiella screening assay targeting the phoE (phosphate porin) gene was used in combination with restriction digest analysis and sequencing to confirm the presence of K. granulomatis.ResultsThe Klebsiella screening assay tested positive in 19/974 (2.0%) genital ulcer specimens. Restriction digest analysis and nucleotide sequencing of the phoE gene confirmed that none of these specimens was positive for K. granulomatis DNA. Similarly, Donovan bodies were not identified in the Giemsa stained ulcer smears of these specimens.ConclusionsThis is the first study to assess K. granulomatis as a cause of genital ulceration in South Africa over a 12-year surveillance period using molecular methods. The results demonstrate that K. granulomatis is no longer a prevalent cause of GUD in our population.