Improving Soluble Expression of SARS-CoV-2 Spike Priming Protease TMPRSS2 with an Artificial Fusing Protein.

SARS-CoV-2 relies on the recognition of the spike protein by the host cell receptor ACE2 for cellular entry. In this process, transmembrane serine protease 2 (TMPRSS2) plays a pivotal role, as it acts as the principal priming agent catalyzing spike protein cleavage to initiate the fusion of the cell membrane with the virus. Thus, TMPRSS2 is an ideal pharmacological target for COVID-19 therapy development, and the effective production of high-quality TMPRSS2 protein is essential for basic and pharmacological research. Unfortunately, as a mammalian-originated protein, TMPRSS2 could not be solubly expressed in the prokaryotic system. In this study, we applied different protein engineering methods and found that an artificial protein XXA derived from an antifreeze protein can effectively promote the proper folding of TMPRSS2, leading to a significant improvement in the yield of its soluble form. Our study also showed that the fused XXA protein did not influence the enzymatic catalytic activity; instead, it greatly enhanced TMPRSS2's thermostability. Therefore, our strategy for increasing TMPRSS2 expression would be beneficial for the large-scale production of this stable enzyme, which would accelerate aniti-SARS-CoV-2 therapeutics development.