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Cytoplasmic dynein is a motor protein that plays a role in a number of cellular processes including retrograde transport. In many cases, dynein needs to interact with another protein, dynactin, to be fully active. An important step in the assembly of the dynein/dynactin complex is the interaction between the N‐terminal portion of the intermediate chain (IC) subunit of dynein and the coiled‐coil 1B (CC1B) region of the p150^Glued subunit of dynactin. Despite evidence for this interaction from binding studies, the exact location of where these proteins bind has remained elusive due to the dynamic nature of the interaction and the presence of intrinsically disordered regions in IC. By using intermolecular paramagnetic relaxation enhancements, we have been able to constrain the location of IC binding on p150^Glued to a position that is different from what has recently been hypothesized in a model of the dynein/dynactin complex based on cryo‐electron microscopy (cryo‐EM) data and AlphaFold predictions. In addition, although phosphorylation is important for regulating dynein/dynactin interactions, we show that a phosphomimetic mutation of IC is not sufficient to alter binding with p150^Glued. 

χ-Conotoxins are known for their ability to selectively inhibit norepinephrine transporters, an ability that makes them potential leads for treating various neurological disorders, including neuropathic pain. PnID, a peptide isolated from the venom of Conus pennaceus, shares high sequence homology with previously characterized χ-conotoxins. Whereas previously reported χ-conotoxins seem to only have a single native disulfide bonding pattern, PnID has three native isomers due to the formation of different disulfide bond patterns during its maturation in the venom duct. In this study, the disulfide connectivity and three-dimensional structure of these disulfide isomers were explored using regioselective synthesis, chromatographic coelution, and solution-state nuclear magnetic resonance spectroscopy. Of the native isomers, only the isomer with a ribbon disulfide configuration showed pharmacological activity similar to other χ-conotoxins. This isomer inhibited the rat norepinephrine transporter (IC50 = 10 ± 2 µM) and has the most structural similarity to previously characterized χ-conotoxins. In contrast, the globular isoform of PnID showed more than ten times less activity against this transporter and the beaded isoform did not display any measurable biological activity. This study is the first report of the pharmacological and structural characterization of an χ-conotoxin from a species other than Conus marmoreus and is the first report of the existence of natively-formed conotoxin isomers.