Ubiquitous endoprotease within constitutive secretory pathways capable of cleavage at the RX(K/R)R consensus motif. Mediates processing of TGFB1, an essential step in TGF-beta-1 activation. Converts through proteolytic cleavage the non-functional Brain natriuretic factor prohormone into its active hormone BNP(1-32). By mediating processing of accessory subunit ATP6AP1/Ac45 of the V-ATPase, regulates the acidification of dense-core secretory granules in islets of Langerhans cells.; (Microbial infection) Cleaves and activates diphtheria toxin DT.; (Microbial infection) Cleaves and activates anthrax toxin protective antigen (PA).; (Microbial infection) Cleaves and activates HIV-1 virus Envelope glycoprotein gp160.; (Microbial infection) Required for H7N1 and H5N1 influenza virus infection probably by cleaving hemagglutinin.; (Microbial infection) Able to cleave S.pneumoniae serine-rich repeat protein PsrP.; (Microbial infection) Facilitates human coronaviruses EMC and SARS-CoV-2 infections by proteolytically cleaving the spike protein at the monobasic S1/S2 cleavage site. This cleavage is essential for spike protein-mediated cell-cell fusion and entry into human lung cells.; (Microbial infection) Facilitates mumps virus infection by proteolytically cleaving the viral fusion protein F.