Biochemical,functional and structural characterization of Akbu-LAAO: A novel snake venom l-amino acid oxidase from Agkistrodon blomhoffii ussurensis

An l-amino acid oxidase (Akbu-LAAO) was isolated from the venom of Agkistrodon blomhoffii ussurensis snake using DEAE Sephadex A-50 ion-exchange, Sephadex G-75 gel filtration, and high performance liquid chromatographies. The homogeneity and molecular mass of Akbu-LAAO were analyzed by SDS-PAGE and MALDI-TOF spectrometry. The sequences of ten peptides from Akbu-LAAO were established by HPLC-nESI-MS/MS analysis. Protein sequence alignment indicated that i) that Akbu-LAAO is a new snake venom LAAO, and ii) Akbu-LAAO shares homology with several LAAOs from the venoms of Calloselasma rhodost, Agkistrodon halys, Daboia russellii siamensis, and Trimeresurus stejnegeri. Akbu-LAAO is a homodimer with a molecular mass of ∼124.4 kDa. It reacts optimally with its enzymatic substrate, Leu, at pH 4.7 with a K_m of 2.1 mM. ICP-AES measurements showed that Akbu-LAAO contains four Zn²⁺ per dimer that are unessential for the hydrolytic activity of the enzyme. The emission fluorescence intensity of Akbu-LAAO decreases by 61% on removal of Zn²⁺ indicating that the zinc probably helps maintain the structural integrity of the enzyme. The addition of exogenous metal ions, including Mg²⁺, Mn²⁺, Ca²⁺, Ce³⁺, Nd³⁺, Co²⁺ and Tb³⁺, increases the l-Leu hydrolytic activity of the enzyme. Akbu-LAAO shows apparent anti-aggregation effects on human and rabbit platelets. It exhibits a strong bacteriostasis effect on Staphylococcus aureus, eighteen fold that of cephalosporin C under the same conditions. Taken together, the biochemical, proteomic, structural and functional characterizations reveal that Akbu-LAAO is a novel LAAO with promise for biotechnological and medical applications.