2 have less basic amino acids residues in the C-terminal region when compared with Kv1.3 high affinity toxins. Such statements could be confirmed in the current work, since Ts15, which has 7 basic residues in its primary structure (Fig. 2) and only 1 in the C-terminal region, shows 5-FU solubility dmso a higher blocking effect to Kv1.2 isoform. Since the amino acid sequence of Ts15 shows a low similarity with that of other toxins, the presence of a functional dyad could not be determined by molecular modeling. To this end NMR or crystallographic studies will be essential. Extensive studies have shown an increasing interest for highly specific blockers of Kv1.3 channels. Since this isoform plays an important

role in the regulation of membrane potential and calcium signaling in lymphocytes cells, it can be used as a therapeutic target for immunosuppressants (Gutman et al., 2005 and Beeton et al., 2006). On the other hand, the

therapeutic application of Kv1.2 blockers is not well elucidated, in view of the fact that this subtype is widespread in the central nervous system and is also able to PLX3397 supplier form heterotetramer channels (Coleman et al., 1999 and Corzo et al., 2008). It is assumed that this subtype is responsible for maintaining the membrane potential and modulation of electrical excitability in neurons and muscle, however the pharmacological properties can vary between heterotretameric and homotetrameric channels (Coleman et al., 1999 and Gutman et al., 2005). In the present study, we have reported mafosfamide that Ts15 is capable of blocking both Kv1.2 and Kv1.3 channels with a higher efficiency for the Kv1.2 isoform (Fig. 3 and Fig. 4). Ts15 can be a potential model for the development of new therapeutic drugs. The significant differences in affinity and blocking efficiency observed,

not only between Kv1.2 and Kv1.3, but among all isoforms tested, can be useful to establish critical residues of channel/toxin interaction and therefore help to design a highly specific ligand for a particular channel subtype. Additionally, the low primary structure similarity found between Ts15 and the known KTxs, justifying its classification into a new subfamily, may unveil the existence of other unknown regions and/or important residues for the toxin/channel interaction. The poor specific ligand/channel binding can result in adverse side effects. For instance, Kaliotoxin 1 inhibits Kv1.3 in the process to suppress T cell activity, but is also capable to block Kv1.1 with a potency enough to produce undesirable side effects, such as diarrhea (Crest et al., 1992, Vianna-Jorge et al., 2003 and Beeton et al., 2006). Recently, Takacs et al. (2009), reported the design of a specific ligand able to inhibit Kv1.3 without increasing gastrointestinal mobility due to off–target interactions with Kv1.1. Those studies highlight the importance to define the critical residues for toxin/channel interaction and therefore provide information to design new therapeutic drugs.