A novel plasminogen activator from Agkistrodon blomhoffii Ussurensis venom (ABUSV-PA): Purification and characterization

A plasminogen activator with arginine ester hydrolysis activity (ABUSV-PA) has been identified and purified to homogeneity from Chinese Agkistrodon blomhoffii Ussurensis snake venom. ABUSV-PA, a monomeric protein with molecular mass of 27815.2 Da, was purified 180-fold with 0.02% recovery for protein and 3.6% recovery for esterase activity. ABUSV-PA reacts optimally with its substrate Nα-tosyl-l-arginine-methyl ester (TAME) at ∼pH 7.5 and at 51 °C. Measurement from inductively coupled plasma-atomic emission spectroscopy (ICP-AES) reveals that ABUSV-PA is a Zn2+-containing protein with a stoichiometry of 1:1 [Zn2+]:[ABUSV-PA]. Analyses of esterase hydrolysis and UV absorption and CD spectra indicate that Zn2+ plays an important role in maintaining the structural integrity rather than the esterase activity of ABUSV-PA. Divalent metal ions, including Ca2+, Mg2+, Cu2+, Ni2+, Mn2+, and Co2+, increase the TAME hydrolysis activity of ABUSV-PA. A red-shift of the emission wavelengths of the synchronous fluorescence of ABUSV-PA, compared to those of free Tyr and Trp, indicates a conformation where the Tyr and Trp residues are in exposed hydrophilic environments. The presence of zinc increases the hydrophobicity of the conformational environments surrounding the Trp residues of ABUSV-PA and affects the secondary structure of ABUSV-PA, as proved by UV absorption and CD spectroscopy.