BJ-48, a novel thrombin-like enzyme from the Bothrops jararacussu venom with high selectivity for Arg over Lys in P1: Role of N-glycosylation in thermostability and active site accessibility

Abstract

BJ-48, a serine protease from the venom of Bothrops jararacussu, was purified to homogeneity using affinity chromatography on p-aminobenzamidine-agarose followed by HPLC gel filtration. BJ-48 presented 52 kDa by SDS–PAGE analysis and 48,036 Da by electron spray mass spectrometry. The enzyme was shown to be highly glycosylated with 42% of N-linked carbohydrates composed of Fuc(1):GalN(4):GlcN(5):Gal(1):Man(2) and a high content of sialic acid residues (8–12%). BJ-48 had optimal esterase activity at pH 7.5 and displayed maximum catalytic rate at 50 °C. Its hydrolytic activity was strongly inhibited by aprotinin and dithiothreitol while N-tosyl- l-phenylalanine chloromethyl ketone, 6-aminocaproic acid, E-64 and soybean trypsin inhibitor (SBTI) were ineffective. The kinetics of BJ-48 with chromogenic substrates revealed an unprecedented selectivity (10 4-fold) for Arg over Lys in P1. BJ-48 proved to be a thrombin-like enzyme (TLE) with a specific fibrinogen-clotting activity of 73.4 NIH units/mg. The TLE rapidly digested human fibrinogen B β chain, but the A α chain was cleaved specifically to release fibrinopeptide A with k cat/ K m=2.1 μM −1 s −1. The TLE showed no activity toward other thrombin substrates like protein C, protease-activated receptor-1 or inhibitors such as hirudin and antithrombin. A non-denaturing procedure using PNGase F and neuraminidase followed by hydrophobic interaction chromatography was employed to obtain active BJ-48 forms with variable carbohydrate content. Compared to the native enzyme, total or partially deglycosylated BJ-48 forms presented up to 2-fold reduction in their specific activities upon heating at 55/65 °C or treatment with SBTI. These results point out a role for BJ-48 glycosylation in thermostability and controlling the access of some canonical protein inhibitors to the active site.