Protein and Peptide Letters - Volume 23, Issue 8, 2016

It is becoming increasingly clear that plants ranging across the plant kingdom produce anionic host defence peptides (AHDPs) with potent activity against a wide variety of human cancers cells. In general, this activity involves membrane partitioning by AHDPs, which leads to membranolysis and / or internalization to attack intracellular targets such as DNA. Several models have been proposed to describe these events including: the toroidal pore and Shai-Matsuzaki- Huang mechanisms but, in general, the mechanisms underpinning the membrane interactions and anticancer activity of these peptides are poorly understood. Plant AHDPs with anticancer activity can be conveniently discussed with reference to two groups: cyclotides, which possess cyclic molecules stabilized by cysteine knot motifs, and other ADHPs that adopt extended and -helical conformations. Here, we review research into the anticancer action of these two groups of peptides along with current understanding of the mechanisms underpinning this action.

It is high time now to discover novel drugs due to the increasing rate of drug resistance by the pathogen organisms and target cells as well as the dependence or tolerance of the body towards the drug. As it is obvious that significant numbers of the modern day pharmaceuticals are derived from natural products, it is equally astonishing to accept that venoms of various origins have therapeutic potentials. Wasp venoms are also a rich source of therapeutically important toxins which includes short cationic peptides, kinins, polyamines and polyDNA viruses, to name a few indentified. Wasp venom cationic peptides, namely mastoparan and its analogs, show a very important potency as an antimicrobial and anticancer agents of the future. They have proven to be the better candidates due to their lesser toxic effects and higher selectivity upon chemical modification and charge optimization. They also have superiority over the conventional chemical drugs as the target cells very rarely develop resistance against them because these peptides primarily imparts its effect through biophysical interaction with the target cell membrane which is dependent upon the net charge of the peptide, its hydrophobicity and anionicity and fluidity of the target cell membranes. Besides, the other components of wasp venom such as kinins, polyamines and polyDNA viruses show various pharmacological promise in the treatment of pain, inflammatory disease, and neurodegenerative diseases such as epilepsy and aversion.

Ribosome-inactivating proteins have been isolated from Trichosanthes kirilowii root tubers and seeds, including trichosanthin, karasurin and T 33 from root tubers and trichosanthrip, trichokirin, alpha-kirilowin, beta-kirilowin and trichoanguin from seeds. The aforementioned proteins show structural and functional similarities. Among them trichosanthin is the best known and most intensely studied. Trichosanthin manifests anticancer activity in vitro and in tumor bearing mice against a variety of cancers/cancer cell lines. It also exhibits anti-HIV-1 and anti-HSV-1 activities. Trichosanthin has been found to be useful for treatment of cesarean scar pregnancies and ectopic pregnancy, and for preventing acute rejection of major histocompatibility complex-mismatched mouse skin allograft. Trichosanthin selectively lesions some neurons and thus can be used in neuroscience research.

The venoms of spiders and scorpions contain a variety of chemical compounds. Antimicrobial peptides (AMPs) from these organisms were first discovered in the 1990s. As of May 2015, there were 42 spider's and 63 scorpion's AMPs in the Antimicrobial Peptide Database (http://aps.unmc.edu/AP). These peptides have demonstrated broad or narrow-spectrum activities against bacteria, fungi, viruses, and parasites. In addition, they can be toxic to cancer cells, insects and erythrocytes. To provide insight into such an activity spectrum, this article discusses the discovery, classification, structure and activity relationships, bioinformatics analysis, and potential applications of spider and scorpion AMPs. Our analysis reveals that, in the case of linear peptides, spiders use both glycine-rich and helical peptide models for defense, whereas scorpions use two distinct helical peptide models with different amino acid compositions to exert the observed antimicrobial activities and hemolytic toxicity. Our structural bioinformatics study improves the knowledge in the field and can be used to design more selective peptides to combat tumors, parasites, and viruses.

This review discusses the importance and properties of antimicrobial peptides from frogs and their synthetic analogues as potential therapeutic alternatives in fighting not only bacterial infections, but also protozoans involved with the major neglected diseases, which afflict human populations (e.g., Chagas disease, African sleeping sickness, Leishmaniasis and malaria). Here, we emphasize their multifunctional properties such as promising broad-spectrum drugs that target protozoan parasites too.

Due to the growing problem of antibiotic-resistant microorganisms, the development of novel antimicrobial agents is a very important challenge. Dimerization of cationic antimicrobial peptides (cAMPs) is a potential strategy for enhancing antimicrobial activity. Here, we studied the effects of magainin 2 (MG2) dimerization on its structure and biological activity. Lysine and glutamic acid were used to synthesize the C- and N-terminal dimers of MG2, respectively, in order to evaluate the impact of linker position used to obtain the dimers. Both MG2 and its dimeric versions showed a random coil structure in aqueous solution. However, in the presence of a structure-inducing solvent or a membrane mimetic, all peptides acquired helical structure. N-terminal dimerization did not affect the biological activity of the peptide. On the other hand, the C-terminal dimer, (MG2)2K, showed antimicrobial activity 8–16 times higher than that of MG2, and the time required to kill Escherichia coli was lower. The enhanced antimicrobial activity was related to membrane permeabilization. (MG2)2K was also more active against multidrug-resistant bacteria of clinical origin. Overall, the results presented here demonstrate that C-terminal lysine-linked dimerization improve the activity of MG2, and (MG2)2K can be considered as a potential antimicrobial agent.

The variety of proteins and peptides isolated from honey bee venom and wasp venom includes melittin, adiapin, apamine, bradykinin, cardiopep, mast cell degranulating peptide, mastoparan, phospholipase A2 and secapin. Some of the activities they demonstrate may find therapeutic applications.

Ubiquitin-like proteins play important roles in diverse biological processes. In Mycobacterium tuberculosis, Pup (prokaryotic ubiquitin-like protein), a functional homologue of eukaryotic ubiquitin, interacts with the proteasome ATPase subunit Mpa to recognize and unfold substrates, and then translocate them into the proteasome core for degradation. Previous studies revealed that, Pup, an intrinsically disordered protein (IDP), adopts a helical structure upon binding to the N-terminal coiled-coil domain of Mpa, at its disordered C-terminal region. In the present study, using circular dichroism (CD), surface plasmon resonance (SPR) and nuclear magnetic resonance (NMR), we show that membrane mimetic and acidic conditions also induce Pup to adopt helical conformations. Moreover, at low pH, Pup, via both of its N- and C-terminal regions, binds to Mpa on sites from the N-terminal region in addition to the C-terminal region of the coiled-coil domain. Our results imply Pup may play undiscovered roles in some biological processes e.g. those involve in membrane.

As an important pro-inflammatory cytokine, interleukin-1beta (IL-1β) participates in a variety of physiological and pathological responses. In order to obtain higher yielded recombinant human interleukin-1 beta (rhIL-1β), we cloned hIL-1β cDNA sequences based on the coding sequence of human mature IL-1. After recombinant pPICZA/hIL-1β was separated and sequenced, we transformed recombinant pPICZA/hIL-1β into Pichia pastoris GS115, SMD1168 and X-33 strain via electroporation. The results showed that recombinant pPICZA/ hIL-1β had the highest expression level in X-33 Pichia pastoris. Subsequently, rhIL-1β was purified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and identified by Western blot. Then the fermentation process was optimized to increase product yield. Under the fermentation conditions of the absorption value of fermentation liquor before induction of 600, oxygen concentration of 20%, methanol concentration of 0.25% with pH 5.0, the yield of rhIL-1β reached to 250 mg/L after 72 h induction at 26°C. After aqueous two-phase extraction combined with chromatography, the purity of rhIL-1β was 95% and the yield was up to 85%. The biological activity of rhIL-1β was detected by MTT assay, and the result showed that rhIL-1 significantly inhibited the growth and proliferation of B16 melanoma cells.