ABSTRACT
The neurotoxic cone snail peptide µ-GIIIA specifically blocks skeletal muscle voltage-gated sodium (NaV1.4) channels. The related conopeptides µ-PIIIA and µ-SIIIA, however, exhibit a wider activity spectrum by also inhibiting the neuronal NaV channels NaV1.2 and NaV1.7. Here we demonstrate that those µ-conopeptides with a broader target range also antagonize select subtypes of voltage-gated potassium channels of the KV1 family: µ-PIIIA and µ-SIIIA inhibited KV1.1 and KV1.6 channels in the nanomolar range, while being inactive on subtypes KV1.2-1.5 and KV2.1. Construction and electrophysiological evaluation of chimeras between KV1.5 and KV1.6 revealed that these toxins block KV channels involving their pore regions; the subtype specificity is determined in part by the sequence close to the selectivity filter but predominantly by the so-called turret domain, i.e. the extracellular loop connecting the pore with transmembrane segment S5. Conopeptides µ-SIIIA and µ-PIIIA, thus, are not specific for NaV channels, and the known structure of some KV channel subtypes may provide access to structural insight into the molecular interaction between µ-conopeptides and their target channels.
Subject(s)
Conotoxins/chemistry , Kv1.1 Potassium Channel/antagonists & inhibitors , Kv1.2 Potassium Channel/antagonists & inhibitors , Kv1.4 Potassium Channel/antagonists & inhibitors , Kv1.6 Potassium Channel/antagonists & inhibitors , Potassium Channel Blockers/chemistry , Shaker Superfamily of Potassium Channels/antagonists & inhibitors , Electrophysiology , HEK293 Cells , Humans , Neurons/metabolism , Peptides/chemistry , Protein DomainsABSTRACT
A total synthesis of the proposed structures of fulicineroside and its aglycone fulicinerine is reported. The tetrasubstituted dibenzofuran substructure was accessible either through a Pd-mediated ortho-metalation or by an Ir-catalyzed meta-borylation. The synthesis of the ß,ß,α-linked trisaccharide consisting of D-olivose, L-rhodinose, and L-rhamnose was challenged by the unprecedented ß-linked rhodinose. A Pd-catalyzed ß-selective glycosylation of a 4-epi-rhodinose and a subsequent Mitsunobu inversion provided selectively the ß-linked L-rhodinose-L-rhamnose disaccharide. Comparison with the reported data for the natural product and the aglycone suggests a misassignment of the structure of the natural product.
