, 2010). Interesting, the results presented here for the MjTX-II can clarify this issue. As discussed in the item 3.2,

the structure of MjTX-II presents PEG4K molecules in its hydrophobic channels at the same regions where fatty acids are found in the MjTX-II/stearic acid structure. Therefore, this finding suggests that the Cys29-Lys122 interaction is not exclusive for Lys49-PLA2s-fatty acid bound structures. Additionally, comparison between BthTX-I/PEG4K (Fernandes et al., 2010) and MjTX-II/PEG4K (this work) structures reveals important features of MjTX-II in comparison to BthTX-I and other bothropic Lys49-PLA2s myotoxins. Despite the high sequential and structural similarity between MjTX-II and BthTX-I

(they share 95% of identity), MAPK inhibitor and the presence of two PEG4K molecules in the hydrophobic channels of both structures, their superposition clearly demonstrates the ligand way of binding at these proteins are somewhat different (Fig. 1C). The reason seems to be the insertion of the residue Asn120 and the Leu32Gly mutation since these characteristics apparently shifts the orientation of PEG molecules inside the hydrophobic channel by modification of the channel ends. Interestingly, Asn120 insertion and Leu32Gly mutation are only found in MjTX-II when comparing this protein to all the other bothropic Lys49-PLA2s whose structures are solved to date (Fig. 4). Therefore, the Asn120 insertion is probably the responsible for the binding of the Afatinib mouse interchain PEG 3 molecule since this insertion leads to a distortion of the protein protomers (Table 3). This evidence is enhanced by the fact that other Lys49-PLA2s toxins that presents 121 amino acids do not bind this interchain PEG4K or PEG3350 (Fernandes et al., 2010) whereas MjTX-II (122 residues) Glutamate dehydrogenase allow a PEG4K interaction at this region. It is important to highlight that bothropic Lys49-PLA2s

that do not have structures solved yet but present mutations and/or insertions at the positions 32 and 120 are known (Fig. 4); however their structural characteristics upon ligand binding will just be evidenced when these structures are elucidated. The C-termini of Lys49-PLA2s toxins has been pointed as containing their myotoxic site (Arni and Ward, 1996, Magro et al., 2003 and Ward et al., 2002). Afterward, dos Santos and colleagues reviewed several native and complexed Lys49-PLA2s and proposed that Arg118, Lys20 and Lys115 residues constitute these toxins myotoxic site (dos Santos et al., 2009). In the same study, the authors propose a two-step mechanism for Lys49-PLA2s which allow the destabilization of biological membranes. The first step of the mechanism would be the interaction of the Lys20, Lys115 and Arg118 of these proteins with the phospholipid head group region (dos Santos et al.