L-amino Acid Oxidase: One of the Many Snake Venoms

Introduction

In snakes, there are a variety of venom families; specifically L-amino acid oxidases (LAAOs) are a group of proteins found mainly in snake venoms (Du and Clemetson, 2002). These proteins are flavoenzymes (can either have FMN or FAD binding glycoproteins) that have elevated levels of activity in snakes such as Elapidae, Viperidae, and Crotalidae (Joosten and van Berkel, 2007; Sajevic et al., 2011). The venoms induce apoptosis of vascular endothelial cells, human embryonic kidney cells, human T-cell leukemia and other cells that eventually lead to haemorrhage (Sajevic et al., 2011). LAAO can also be found in fungi, bacteria and plants, though they no longer act as toxins and instead are involved with nitrogen use (Du and Clemetson, 2002).
In this analysis, eight sequences were used to evaluate the evolution of L-amino acid oxidase as venom in snakes (Table 1). Five of the snakes belonged to the Viperidae family and the two other belonged to the Elapidae family. Since LAAO is commonly found in these two families as venom, they should probably have a close relationship to each other. For the analysis of selection, the null hypothesis was that this protein might not be under selective pressure (neutrality) and the alternative hypothesis was that the protein might be under some directional selection (positive or purifying). In order to assess the relationship between the eight organisms, phylogenetic trees of LAAO for the eight sequences (both DNA and protein) were constructed in MEGA using the Neighbor-Joining Tree option (Figure 1 & 2). Gallus gallus (chicken) was used as the out-group (Table 1, Figure 1 & 2).


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