Effect of polyethylene glycol 20 000 on protein extraction efficiency of formalin-fixed paraffin-embedded tissues in South Africa

Background: Optimal protocols for efficient and reproducible protein extraction from formalin-fixed paraffin-embedded (FFPE) tissues are not yet standardised and new techniques are continually developed and improved. The effect of polyethylene glycol (PEG) 20 000 on protein extraction efficiency has not been evaluated using human FFPE colorectal cancer tissues and there is no consensus on the protein extraction solution required for efficient, reproducible extraction.Objective: The impact of PEG 20 000 on protein extraction efficiency, reproducibility and protein selection bias was evaluated using FFPE colonic tissue via liquid chromatography tandem mass spectrometry analysis.Methods: This study was conducted from August 2017 to July 2019 using human FFPE colorectal carcinoma tissues from the Anatomical Pathology department at Tygerberg Hospital in South Africa. Samples were analysed via label-free liquid chromatography tandem mass spectrometry to determine the impact of using PEG 20 000 in the protein extraction solution. Data were assessed regarding peptide and protein identifications, method efficiency, reproducibility, protein characteristics and organisation relating to gene ontology categories.Results: Polyethylene glycol 20 000 exclusion increased peptides and proteins identifications and the method was more reproducible compared to the samples processed with PEG 20 000. However, no differences were observed with regard to protein selection bias. We found that higher protein concentrations ( 10 µg) compromised the function of PEG.Conclusion: This study indicates that protocols generating high protein yields from human FFPE tissues would benefit from the exclusion of PEG 20 000 in the protein extraction solution.

A novel approach for selecting potent peptide inhibitors of the SARS-CoV2-Mpro protease

Here, we describe a new high throughput selection technology for identifying exceedingly specific and effective peptide inhibitors. This technology incorporates the co-expression of a cytotoxic protein and a library of peptide variants inserted directly into a loop of a carrier protein. Selection is based on the cytotoxicity neutralization by a member of a peptide library binding to and inhibiting the cytotoxic protein. Our technology provides the flexibility of screening both cyclic and linear peptides. Herein, we demonstrate the power of this technology by developing selective inhibitors of the main coronavirus protease (Mpro) in a matter of weeks by screening libraries of cyclic and linear peptides. This technology opens up an opportunity to develop inhibitors for a wide range of previously undruggable targets.