Background The venoms of predators such as spiders, scorpions, cone snails, sea anemones, and snakes, have been an excellent source of pharmacological diversity for drug discovery and as pharmacological tools for elucidating the structure, function, and physiological properties of ion channels. Here we describe the first known peptide antagonist of the nociceptor ion channel transient receptor potential ankyrin 1 (TRPA1). Results We constructed a recombinant cDNA library encoding ∼100 diverse GPI-anchored peptide toxins (t-toxins) derived from spider venoms and screened this library by co-expression in Xenopus oocytes with TRPA1. This screen resulted in identification of protoxin-I (ProTx-I), a 35-residue peptide from the venom of the Peruvian green-velvet tarantula, Thrixopelma pruriens, as the first known high-affinity peptide TRPA1 antagonist. Interestingly, ProTx-I was previously identified as an antagonist of voltage-gated sodium (NaV) channels. To identify the surfaces of ProTx-I by which it binds to these distinct ion channel types, we constructed a t-toxin library of ProTx-I alanine-scanning mutants and screened this library against NaV1.2 and TRPA1. This revealed distinct partially overlapping surfaces of ProTx-I by which it binds to these two ion channels, and whose specific chemical features explain its higher affinity for NaV1.2 than for TRPA1. Importantly, this mutagenesis yielded two novel ProTx-I variants that are only active against either TRPA1or NaV1.2, but not both. By testing its activity against chimeric channels, we identified the extracellular loops of the TRPA1 S1-S4 gating domain as the ProTx-I binding site. Conclusions These studies establish screening of t-toxin libraries of native and mutated toxins, which we term “toxineering”, as a generally applicable method for isolation of novel ion channel modifiers and for design of ion channel modifiers with altered target selectivity. They also suggest that ProTx-I will be a valuable pharmacological reagent for addressing the biophysical mechanisms of TRPA1 gating, the physiology and pathophysiology of TRPA1 function in nociceptors, and for potential clinical application in the context of pain and inflammation.

Highlights d HAT1 is an EGF-stimulated acetyltransferase required for EGF-dependent growth d HAT1 holoenzyme specifically binds to histone H4 promoters d Histone H4 promoters contain an acetate-sensitive genomic element d HAT1 expression is associated with poor cancer outcomes in humans and mice

Non-receptor protein tyrosine kinases (NRTKs) are essential for cellular homeostasis, and thus are a major focus of current drug discovery efforts. Peptide substrates that can enhance lanthanide ion luminescence upon tyrosine phosphorylation enable rapid, sensitive screening of kinase activity, however design of suitable substrates that can distinguish between tyrosine kinase families is a huge challenge. Despite their different substrate preferences, many NRTKs are structurally similar even between families. Furthermore, the development of lanthanide-based kinase assays is hampered by incomplete understanding of how to integrate sequence selectivity with metal ion binding, necessitating laborious iterative substrate optimization. We used curated proteomic data from endogenous kinase substrates and known Tb3+-binding sequences to build a generalizable in silico pipeline with tools to generate, screen, align and select potential phosphorylation-dependent Tb3+-sensitizing substrates that are most likely to be kinase specific. We demonstrated the approach by developing several substrates that are selective within kinase families and amenable to HTS applications. Overall, this strategy represents a pipeline for developing efficient and specific assays for virtually any tyrosine kinase that use high throughput screening-compatible lanthanide-based detection. The tools provided in the pipeline also have the potential to be adapted to identify peptides for other purposes, including other enzyme assays or protein binding ligands.

Disruption of regulatory protein phosphorylation can lead to disease, and is particularly prevalent in cancers. Inhibitors that target deregulated kinases are therefore a major focus of chemotherapeutic development. Achieving sensitivity and specificity in high-throughput compatible kinase assays is key to successful inhibitor development. Here we describe the application of time-resolved luminescence detection to the direct sensing of Syk kinase activity and inhibition using a novel peptide substrate. Chelation and luminescence sensitization of Tb3+ allowed the direct detection of peptide phosphorylation without any antibodies or other labeling reagents. Characterizing the Tb3+ coordination properties of the phosphorylated vs. unphosphorylated form of the peptide revealed that an inner-sphere water was displaced upon phosphorylation, which likely was responsible for both enhancing the luminescence intensity and also extending the lifetime, which enabled gating of the luminescence signal to improve the dynamic range. Furthermore, a shift in the optimal absorbance maximum for excitation was observed, from 275 nm (for the unphosphorylated tyrosine peptide) to 266 nm (for the phosphorylated tyrosine peptide). Accordingly, time-resolved measurements with excitation at 266 nm via a monochromator enabled a 16-fold improvement in base signal to noise for distinguishing phosphopeptide from unphosphorylated peptide. This led to a high degree of sensitivity and quantitative reproducibility, demonstrating the amenability of this method to both research laboratory and high-throughput applications.