There is a methionine (Met450) residue in a similar position to the Met181 residues of NavAb, as shown in the sequence alignment in Table 1. However, in Kv1.3, these methionine residues are acting to stabilize the channel and therefore cannot flip
outwards towards the fullerene. In contrast to NavAb, these methionine residues are unable to form a hydrophobic interaction with the Selleck HDAC inhibitor [Lys]-see more fullerene surface, as shown in Figure 4. Amino acid sequences of the NavAb and Kv1.3 ion channels were obtained from the National Center for Biotechnology Information (NCBI) protein database (NCBI:3RVY_A, NCBI:NP_002223.3, respectively) . The sequences were aligned using multiple sequence comparison by log-expectation (MUSCLE) . Figure 4 Side view of the binding of [Lys]-fullerene to the outer vestibule of Kv1.3. The Glu420 residue on chain A is shown in red, and the Met450 residues are shown in grey. Bacterial and mammalian channels differ
significantly in both sequence and structure. In an attempt to understand how the [Lys]-fullerene might bind to a mammalian Nav channel, we align the sequence of NavAb to Nav1.8. Although μ-conotoxin is sensitive to Nav1 channels, Nav1.8 is both tetrodotoxin and μ-conotoxin insensitive [19, 49]. The Nav1.8 sequence has recently been studied for gain-of-function mutations which have been PARP inhibitor linked to painful peripheral neuropathy . A few selective blockers of Nav1.8 have been identified, such as A-803467 and μO-conotoxin, and have been shown to suppress chronic pain behavior [19, 20]. Therefore, it is interesting to consider
the sensitivity of Nav1.8 to [Lys]-fullerene. Amino acid sequences of the NavAb and Nav1.8 ion channels were obtained from the NCBI protein database (NCBI:3RVY_A, NCBI:NP_006505.2, respectively) [35, 50], and the sequences were aligned using MUSCLE . A comparison of the two sequences, shown in Table 1, demonstrates that Glu177 in NavAb aligns with the Asp-Glu-Lys-Ala (DEKA) residues of the selectivity not filter of Nav1.8. As mentioned, the four methionine residues at position 181 form hydrophobic bonds with the fullerene molecule ‘coordinating’ it to the pore of NavAb. In Nav1.8, there are four hydrophobic residues in a similar position to Met181 and in particular Leu-Met-Iso-Leu (LMIL). It may be possible that a similar hydrophobic bond could form between the fullerene and this mammalian Nav channel. However, in Kv1.3, the methionine residue does not contribute to the binding of [Lys]-fullerene and instead stabilizes the channel. A similar mechanism could occur in Nav1.8. Unfortunately, no crystal structure of Nav1.8 or any other mammalian Nav channel is currently available. Therefore, to confirm such a hypothesis requires significant future work such as building a Nav1.8 homology model and conducting molecular dynamics simulations to ascertain the binding affinity of the [Lys]-fullerene.