Transthyretin, a New Cryptic Protease

摘要: Abstract Transthyretin (TTR) is a plasma homotetrameric protein that acts physiologically as transporter of thyroxine (T4) and retinol, in the latter case through binding to retinol-binding (RBP). A fraction TTR carried high density lipoproteins by apolipoprotein AI (apoA-I). We further investigated nature TTR-apoA-I interaction found from different sources (recombinant plasmatic) able process proteolytically apoA-I, cleaving its C terminus after Phe-225. TTR-mediated proteolysis was inhibited serine protease inhibitors (phenylmethanesulfonyl fluoride, Pefabloc, diisopropyl fluorophosphate, chymostatin, Nα-p-tosyl-l-phenylala-nine-chloromethyl ketone), suggesting chymotrypsin-like activity. fluorogenic substrate corresponding an apoA-I fragment encompassing amino acid residues 223-228 (Abz-ESFKVS-EDDnp) used characterize catalytic activity TTR, including optimum reaction conditions (37 °C pH 6.8) constant (Km = 29 μm); when complexed with RBP, lost, whereas T4, only slight decrease observed. Cell lines expressing were degrade Abz-ESFKVS-EDDnp 2-fold more efficiently than control cells lacking expression; this effect reversed presence RBP cell culture media, therefore proving TTR-specific proteolytic can act novel cryptic might have new, potentially important role under physiological and/or pathological conditions.