Engineering of a Spider Peptide via Conserved Structure-Function Traits Optimizes Sodium Channel Inhibition In Vitro and Anti-Nociception In Vivo

Venom peptides are potent and selective modulators of voltage-gated ion channels that regulate neuronal function both in health and in disease. We previously identified the spider venom peptide Tap1a from the Venezuelan tarantula Theraphosa apophysis that targeted multiple voltage-gated sodium and calcium channels in visceral pain pathways and inhibited visceral mechano-sensing neurons contributing to irritable bowel syndrome. In this work, alanine scanning and domain activity analysis revealed Tap1a inhibited sodium channels by binding with nanomolar affinity to the voltage-sensor domain II utilising conserved structure-function features characteristic of spider peptides belonging to family NaSpTx1. In order to speed up the development of optimized Na_V-targeting peptides with greater inhibitory potency and enhanced in vivo activity, we tested the hypothesis that incorporating residues identified from other optimized NaSpTx1 peptides into Tap1a could also optimize its potency for Na_Vs. Applying this approach, we designed the peptides Tap1a-OPT1 and Tap1a-OPT2 exhibiting significant increased potency for Na_V1.1, Na_V1.2, Na_V1.3, Na_V1.6 and Na_V1.7 involved in several neurological disorders including acute and chronic pain, motor neuron disease and epilepsy. Tap1a-OPT1 showed increased potency for the off-target Na_V1.4, while this off-target activity was absent in Tap1a-OPT2. This enhanced potency arose through a slowed off-rate mechanism. Optimized inhibition of Na_V channels observed in vitro translated in vivo, with reversal of nocifensive behaviours in a murine model of Na_V-mediated pain also enhanced by Tap1a-OPT. Molecular docking studies suggested that improved interactions within loops 3 and 4, and C-terminal of Tap1a-OPT and the Na_V channel voltage-sensor domain II were the main drivers of potency optimization. Overall, the rationally designed peptide Tap1a-OPT displayed new and refined structure-function features which are likely the major contributors to its enhanced bioactive properties observed in vivo. This work contributes to the rapid engineering and optimization of potent spider peptides multi-targeting Na_V channels, and the research into novel drugs to treat neurological diseases.

Molecular Analysis of the Clavulanic Acid Regulatory Gene Isolated from an Iranian Strain of Streptomyces Clavuligerus , PTCC 1709

OBJECTIVE

The clavulanic acid regulatory gene (claR) is in the clavulanic acid biosynthetic gene cluster that encodes ClaR. This protein is a putative regulator of the late steps of clavulanic acid biosynthesis. The aim of this research is the molecular cloning of claR, isolated from the Iranian strain of Streptomyces clavuligerus (S. clavuligerus).

MATERIALS AND METHODS

In this experimental study, two different strains of S. clavuligerus were used (PTCC 1705 and DSM 738), of which there is no claR sequence record for strain PTCC 1705 in all three main gene banks. The specific designed primers were subjected to a few base modifications for introduction of the recognition sites of BamHI and ClaI. The claR gene was amplified by polymerase chain reaction (PCR) using DNA isolated from S. clavuligerus PTCC 1705. Nested-PCR, restriction fragment length polymorphism (PCR-RFLP), and sequencing were used for molecular analysis of the claR gene. The confirmed claR was subjected to double digestion with BamHI and ClaI. The cut claR was ligated into a pBluescript (pBs) vector and transformed into E. coli.

RESULTS

The entire sequence of the isolated claR (Iranian strain) was identified. The presence of the recombinant vector in the transformed colonies was confirmed by the colony-PCR procedure. The correct structure of the recombinant vector, isolated from the transformed E. coli, was confirmed using gel electrophoresis, PCR, and double digestion with restriction enzymes.

CONCLUSION

The constructed recombinant cassette, named pZSclaR, can be regarded as an appropriate tool for site directed mutagenesis and sub-cloning. At this time, claR has been cloned accompanied with its precisely selected promoter so it could be used in expression vectors. Hence the ClaR is known as a putative regulatory protein. The overproduced protein could also be used for other related investigations, such as a mobility shift assay.

Recognition of the alternatively spliced segments of fibronectin by the RCJ 3.1C5.18 chondrocytic rat cell line

OBJECTIVES

To define, for the C5.18 chondrocyte-restricted rat cell line, (1) the capacities for recognition of alternatively spliced segments of the adhesion protein fibronectin (FN), (2) the integrin subunits required for such recognition, and (3) differences in such FN recognition vs the multipotential chondroprogenitor line, RCJ 3.1.

METHODS

C5.18 and RCJ 3.1 cells were tested for their capacities to adhere to recombinant alternatively spliced segments of rat FN, presented on plastic surfaces either in isolation or in partial FNs spanning the 7th through 15th type III repeats (III7-15 FNs). The effects on such adhesion of cations and integrin subunit-specific antibodies were tested.

RESULTS

Despite significant augmentation in chondrocyte-specific gene expression in C5.18 relative to the RCJ 3.1 cells, the two lines exhibited similar recognition of FN spliced segments and partial isoforms. Specifically, both lines adhered to the extra type III repeat A (EIIIA) and V, but not extra type III repeat B (EIIIB), segments. There were different cation and integrin subunit requirements for adhesion to EIIIA vs V segments, and only the V segment was recognized in the context of a III7-15 FN. Such recognition was mediated via a "second" arginine-glycine-aspartic acid (RGD) sequence that is present in the V95 subsegment in rat, but not human, FN.

CONCLUSION

The chondrocyte lineage-committed C5.18 cell line, similar to its multipotential chondroprogenitor, RCJ 3.1, recognizes the "cartilage-restricted" EIIIA and V segments of FN with cation, integrin, and molecular context requirements that are specific to each of these segments.