ABSTRACT
L-amino acid oxidase (LAAO) occurs widely in snake venoms. The enzyme is highly specic for L-amino acids, and generally hydrophobic amino acids are the best substrates. LAAO is a avoprotein and consists of two identical subunits, each with a molecular weight of 57-68 kDa. The puried enzymes are glycoproteins with 3 to 4% carbohydrate. Deglycosylation of the enzyme does not alter the enzymatic activity but appears to alter its pharmacological activities. The amino acid
I. Introduction .......................................................................................................................... 222 II. Assay Methods ..................................................................................................................... 222 III. Occurrence in Snake Venoms .............................................................................................. 223 IV. Purication of Snake Venom LAAOs .................................................................................. 223 V. Cloning and Expression of Snake Venom LAAOs ..............................................................224 VI. Physical Properties of Snake Venom LAAOs ......................................................................224 A. General Physical Properties of Snake Venom LAAOs ..................................................224 B. Reconstitution of LAAO ................................................................................................225 VII. The Chemical Structure of LAAOs .....................................................................................225 A. N-terminal Sequences ....................................................................................................225 B. Amino Acid Sequences ..................................................................................................225 C. The Glycan Structure .....................................................................................................226 VIII. Three-Dimensional Structure of LAAOs ............................................................................. 227 A. X-ray Structure of Calloselasma rhodostoma LAAO ................................................... 227 B. Molecular Modeling of Bothrops jararacussu and B. moojeni LAAOs ........................ 227 IX. The Enzymatic Properties of LAAOs ..................................................................................228 A. General Enzymatic Properties .......................................................................................228 B. Substrate Specicity .......................................................................................................228 C. Mechanism of Catalysis .................................................................................................228 X. Immunological Properties of LAAOs .................................................................................. 229 XI. The Pharmacological Activities of LAAOs ......................................................................... 229 A. Edema-Inducing and Hemorrhagic Activities ................................................................230 B. Anticoagulant Effects .....................................................................................................230 C. Effects on Platelet Aggregation ......................................................................................230 D. Apoptosis-Inducing Effect ............................................................................................. 231 E. Antibacterial Activity ..................................................................................................... 231 F. Leishmanicidal Activity ................................................................................................. 232 G. Anti-HIV Activity .......................................................................................................... 232 XII. Conclusions .......................................................................................................................... 232 Acknowledgment ........................................................................................................................... 233 References ...................................................................................................................................... 233
sequences of snake venom LAAOs show a high degree of homology. X-ray structural analysis of LAAO revealed a dynamic active site and the presence of three domains: an FAD-binding domain, a substrate-binding domain, and a helical domain. LAAOs were reported to exhibit moderate lethal toxicity. Recent studies showed that LAAOs are multifunctional enzymes exhibiting edema-inducing, platelet aggregation-inducing or -inhibiting, apoptosis-inducing, as well as antibacterial, anticoagulant, and anti-HIV effects. These effects are mostly mediated by the H2O2 liberated in the oxidation process, but direct interactions between LAAO and the target cells may play an important role. High-resolution x-ray structural analysis of the enzyme revealed the presence of a channel that would direct the H2O2 product to the exterior surface of the protein, near the glycan moiety at Asn 172, which is thought to be involved with LAAO-target cell interaction. This may explain the ability of LAAO to localize H2O2 to the targeted cells. A better understanding of the pharmacological actions of LAAOs will facilitate the application of snake venom LAAOs in the design of anticancer and anti-HIV drugs, as well as drugs for the treatment of infectious diseases caused by parasites such as Leishmania.
