Easy and efficient protocol for purification of recombinant peptides

Efficient expression and purification of tag-free recombinant human procalcitonin (hPCT) with precise sequence in E.coli

We present an efficient method for expression and purification of recombinant human procalcitonin (hPCT) in E. coli T7 express LysY/Iq cells, ensuring precise N- and C-terminal amino acid sequences. Our method involves fusing codon-optimized cDNA with two distinct tag sequences: eXact tag and chitin binding domain (CBD) tag. To purify the protein, we employ a two-step affinity chromatography process. Firstly, we utilize the N-terminal Profinity eXact tag and purify the protein through Profinity eXact-affinity column chromatography using a resin on which a mutant subtilisin protease was immobilized. The eXact tag was removed by adding NaF to activate the enzyme. Subsequently, the digested sample containing C-terminal CBD tag is directly loaded for the second step of chitin affinity chromatography. Elution is achieved through dithiothreitol (DTT)-catalyzed self-cleavage of the intein sequence from the fusion protein. As a result, the target protein is selectively recovered in the flow-through, completely tag-free, with a purity exceeding 95%. To ensure high purity and eliminate potential contaminants, we effectively remove E. coli host DNA and endotoxins through a combination of streptomycin sulfate, Triton X-114, and ammonium sulfate treatment. The exceptional level of purity obtained eliminates the need for further purification steps in most applications. This highly purified hPCT can be used as a calibrator in procalcitonin or calcitonin immunoassays. Notably, our approach effectively manages small peptides that are prone to degradation by E. coli host proteases, offering a robust solution for various research and application requirements.

Calnuc-derived nesfatin-1-like peptide is an activator of tumor cell proliferation and migration

Calnuc (nucleobindin-1, nucb1) is a Ca2+ -binding protein involved in the etiology of many human diseases. To understand the functions of calnuc, we have identified a nesfatin-1-like peptide (NLP) in its N terminus that is proteolyzed by a convertase enzyme in the secretory granules of cells. Mutational studies confirm the presence of a proteolytic cleavage site for proprotein convertase subtilisin/kexin type 1 (PCSK1). We demonstrate that NLP regulates Gαq-mediated intracellular Ca2+ dynamics, likely via a G-protein-coupled receptor. NLP treatment to carcinoma cell lines (SCC131 cells) promotes the expression of regulators of cell cycle, proliferation, and clonogenicity by the AKT/mTOR pathway. NLP is causative of augmented migration and epithelial-mesenchymal transition (EMT), illustrating its metastatic propensity and establishing its tumor promotion ability.

Critical APJ receptor residues in extracellular domains that influence effector selectivity

Human APJ receptor/apelin receptor (APJR), activated by apelin peptide isoforms, regulates a wide range of physiological processes. The role of extracellular loop (ECL) domain residues of APJR in ligand binding and receptor activation has not been established yet. Based on multiple sequence alignment of APJ receptor from various organisms, we identified conserved residues in the extracellular domains. Alanine substitutions of specific residues were characterized to evaluate their ligand binding efficiency and G_q -, G_i -, and β-arrestin-mediated signaling. Mutation-dependent variation in ligand binding and signaling was observed. W¹⁹⁷ A in ECL2 and L²⁷⁶ L²⁷⁷ W²⁷⁹ -AAA in ECL3 were deficient in G_i and β-arrestin signaling pathways with relatively preserved G_q -mediated signaling. T¹⁶⁹ T¹⁷⁰ -AA, Y¹⁸² A, and T¹⁹⁰ A mutants in ECL2 showed impaired β-arrestin-dependent cell signaling while maintaining G protein_- mediated signaling. Structural comparison with angiotensin II type I receptor revealed the importance of ECL2 and ECL3 residues in APJR ligand binding and signaling. Our results unequivocally confirm the specific role of these ECL residues in ligand binding and in orchestrating receptor conformations that are involved in preferential/biased signaling functions.

Molecular determinants on extracellular loop domains that dictate interaction between β-arrestin and human APJ receptor

The human APJ receptor (APJR), activated by apelin isoforms, regulates cardiovascular functions and fluid homeostasis. Understanding its structure-function relationship is crucial for a comprehensive knowledge of signalling aberrations that cause several physiological disorders. Here, we demonstrate the influence of extracellular loop (ECL) domains in the mechanism of β-arrestin-mediated signalling from human APJR: Apelin system. Alanine mutations of evolutionarily conserved residues were characterized using receptor internalization, β-arrestin pull-down, Akt phosphorylation and cell migration assay. C281A and ²⁶⁸ KTL²⁷⁰ -AAA in ECL3 were deficient in all assays, whereas ¹⁸³ MDYS¹⁸⁶ -AAAA mutant in ECL2 showed impaired β-arrestin-mediated signalling but demonstrated G_i -dependent cell migration. Our findings establish that conserved residues in the extracellular domain play a prominent role in modulating receptor interactions with the β-arrestin signalling cascade.

An efficient strategy for heterologous expression and purification of active peptide hainantoxin-IV

Hainantoxin-IV (HNTX-IV) from the venom of the spider Selenocosmia hainana is a potent antagonist that specifically inhibits the tetrodotoxin-sensitive (TTX-S) sodium channels. The toxin peptide consists of 35 amino acids and adopts a typical inhibitory cystine knot (ICK) motif. To obtain adequate HNTX-IV peptides for further insight into the structure-activity relationships of the toxin, a novel strategy including cloning, expression and purification was developed in an E. coli expression system. For this purpose, a seamless restriction-free (RF) cloning method was employed for the construction of an expression vector to avoid introducing unwanted sequences into the target gene. Furthermore, the solubility of recombinant HNTX-IV could be promoted efficiently by the combination of a glutathione S-transferase (GST) tag and a small ubiquitin-related modifier (SUMO) tag. Finally, an affinity-chromatography-free purification strategy was developed by cut-off dialysis tubing combined with trichloroacetic acid (TCA) extraction. Further HPLC purification yielded recombinant, tag-free HNTX-IV with high yield and purity. The molecular weight of recombinant HNTX-IV (rHNTX-IV) is identical to its theoretical value according to Matrix-Assisted Laser Desorption / Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) analysis. The recombinant toxin has similar activity (IC₅₀ value of 120 nM) on the tetrodotoxin-sensitive (TTX-S) sodium channels in adult rat dorsal root ganglion (DRG) neurons to native toxins. In the report, an efficient and cost-effective strategy for producing rHNTX-IV was developed, which paved the way for the further study of structure-activity relationships of rHNTX-IV and its pharmaceutical applications.