RESUMO
Human coronavirus HKU1 (HCoV-HKU1) is associated with respiratory disease and is prevalent worldwide, but in vitro model for virus replication is lacking. Interaction between the coronaviral spike (S) protein and its receptor is the major determinant of virus tissue and host specificity, but virus entry is a complex process requiring a concerted action of multiple cellular elements. Here, we show that KLK13 is required for the infection of the human respiratory epithelium and is sufficient to mediate the entry of HCoV-HKU1 to non-permissive RD cells. We also demonstrated HCoV-HKU1 S protein cleavage by KLK13 in the S1/S2 region, proving that KLK13 is the priming enzyme for this virus. Summarizing, we show for the first time that protease distribution and specificity predetermines the tissue and cell specificity of the virus and may also regulate interspecies transmission. It is also of importance that presented data may be relevant for the emerging coronaviruses, including SARS-CoV-2 and may help to understand the differences in their zoonotic potential.
RESUMO
A series of linear and monocyclic (with a disulfide bridge only) analogues of trypsin inhibitor SFTI-1 modified in the P1 and/or P1' positions were synthesized by the solid-phase method. In the substrate specificity P1 position, Phe or N-benzylglycine (Nphe) were introduced, whereas the conserved Ser6 in Bownam-Birk (BBI) inhibitors was replaced by Hse (L-homoserine), Nhse [N-(2-hydroxyethyl)glycine], Sar, and Ala. Kinetic studies of interaction of the analogues with bovine α-chymotrypsin have shown that in monocyclic (but not linear) analogues, Hse and Nhse are tolerated to afford potent inhibitors. This is the first evidence that the absolutely conserved Ser present in the inhibitor's P1' position can be successfully replaced by a synthetic derivative.
