, 2009 and dos Santos et al., 2011a). Therefore, the hydrophobic channel was demonstrated to be involved in one of the steps required for Lys49-PLA2s action mechanism (dos Santos et al., 2009 and dos Santos et al., 2011a). It is also interesting to highlight that if the alternative dimer is considered as biological dimer, the myotoxic sites from both monomers are aligned at the same plane (side by side) for the complexed structures (active state) and an interchain Tyr119-Tyr119 hydrogen bond is formed (Table 3) which increasing the toxin potency (dos Santos et al., 2009). The sequence alignment of bothropic Lys49-PLA2s (Fig. 4) shows that the residues of the myotoxic site (Lys20, Lys115 Selleck Roxadustat and Arg118) and Tyr119 are

conserved in MjTX-II, however, the interchain Tyr119–Tyr119 hydrogen bond is not present in its dimeric interface (these residues are at a distance of 4.7 Å). Analyzing MjTX-II sequence (Fig. 4) it is possible to observe that the C-terminal region of this toxin presents some particularities as an insertion of a residue at position 120 and a mutation at position 121 (His→Tyr) if compared to other bothropic Lys49-PLA2s whose structures are known. Therefore, Asn120 insertion may be the responsible for a diversion of this region as evidenced by the lack of Tyr119-Tyr119 Selleck BGB324 hydrogen bond which is probably compensated by the creation of two new hydrogen bonds with the participation

of Tyr121 residue (Table 3). Then, taking into account these facts (Asn120 insertion and mutations of residues 32 and 121) and their consequences to PEG4Ks mode of binding,

it is reasonable to suggest that MjTX-II may require specific or modified inhibitors when compared to molecules that are able to inhibit bothropic Lys49-PLA2s by interaction with their hydrophobic channels. This is due to the different profile of ligand binding presented at this region oxyclozanide (Fig. 1C.) and may have implications when considering structure-based ligand design for Lys49-PLA2s. As discussed in the last two sections, MjTX-II structure was solved in the oligomeric assembly known as “alternative dimer” given that it has higher probability of occurrence in solution due to bioinformatic analyses and also due to several experimental and functional reasons (dos Santos et al., 2011a, dos Santos et al., 2009, Fernandes et al., 2010, Marchi-Salvador et al., 2009, Murakami et al., 2005 and Murakami et al., 2007). However, as discussed in a recent review in this field (Lomonte and Rangel, 2012), this subject is still controversial for some authors. Although no experiment was able to definitively prove the correct assembly adopted by Lys49-PLA2s toxins, MjTX-II structure added an important experimental evidence for the choice of the alternative dimer as the probable quaternary assembly found in solution for these proteins. As shown in the Fig. 2, the PEG 3 binds simultaneously to both monomers of the protein.