Bioactive Natural Peptides

Structural Design and Synthesis of Novel Cyclic Peptide Inhibitors Targeting Mycobacterium tuberculosis Transcription

Tuberculosis (TB) remains one of the deadliest infectious diseases in the world. Although several established antitubercular drugs have been found, various factors obstruct efforts to combat this disease due to the existence of drug-resistance (DR) TB strains, the need for lengthy treatment, and the occurrence of side effects from drug–drug interactions. Rifampicin (RIF) is the first line of antitubercular drugs and targets RNA polymerase (RNAP) of Mycobacterium tuberculosis (MTB). Here, RIF blocks the synthesis of long RNA during transcription initiation. The efficacy of RIF is low in DR-TB strains, and the use of RIF leads to various side effects. In this study, novel cyclic peptides were computationally designed as inhibitors of MTB transcription initiation. The designed cyclic peptides were subjected to a virtual screening to generate compounds that can bind to the RIF binding site in MTB RNAP subunit β (RpoB) for obtaining a new potential TB drug with a safe clinical profile. The molecular simulations showed that the cyclic peptides were capable of binding with RpoB mutants, suggesting that they can be possibility utilized for treating DR-TB. Structural modifications were carried out by acetylation and amidation of the N- and C-terminus, respectively, to improve their plasma stability and bioavailability. The modified linear and cyclic peptides were successfully synthesized with a solid-phase peptide synthesis method using Fmoc chemistry, and they were characterized by analytical HPLC, LC-ESI-MS⁺, and 1H NMR.

Antioxidant and angiotensin-converting enzyme (ACE) inhibitory activity of thymosin alpha-1 (Thα1) peptide

In this research, the antioxidant property of thymosin alpha-1 (Thα1) peptide was investigated through various antioxidant methods. Thα1 showed 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (IC₅₀ = 20 µM) and its 2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) scavenging reached 45.33% at 80 µM (IC₅₀ = 85 µM). In addition, hydroxyl and superoxide radical scavenging of Thα1 peptide exhibited a concentration-depended manner. The IC₅₀ values of hydroxyl and superoxide radical scavenging were estimated to be 82 µM and 20 µM, respectively. The effect of Thα1 on eliminating superoxide radicals was higher (62.23%) than other antioxidant assays. Moreover, the antioxidant activity of Thα1 peptide was evaluated by measuring cellular reactive oxygen species (ROS). Results indicated that Thα1 decreased the generation of ROS level in 1321 N1 human neural asterocytoma cells. The inhibitory effect of Thα1 on angiotensin-converting enzyme (ACE) was determined. The kinetic parameters (K_m and V_max) and the inhibition pattern were examined. Based on the Lineweaver-Burk plot, Thα1 displayed a mixed inhibition pattern. The IC₅₀ and K_i values of Thα1 were 0.8 µM and 3.33 µM, respectively. Molecular modeling suggested that Thα1 binds to ACE-domains with higher affinity binding to N-domain with the binding energy of -22.87 kcal/mol. Molecular docking indicated that Thα1 interacted with ACE enzyme (N- and C-domains) due to electrostatic, hydrophobic, and hydrogen forces. Our findings suggested that Thα1 possess a multifunctional peptide with dual antioxidant and ACE-inhibitory properties. Further researches are needed to investigate the antioxidant and anti-hypertensive effect of Thα1 both in vitro and in vivo.

Natural Phyto-Bioactive Compounds for the Treatment of Type 2 Diabetes: Inflammation as a Target

Diabetes is a metabolic, endocrine disorder which is characterized by hyperglycemia and glucose intolerance due to insulin resistance. Extensive research has confirmed that inflammation is closely involved in the pathogenesis of diabetes and its complications. Patients with diabetes display typical features of an inflammatory process characterized by the presence of cytokines, immune cell infiltration, impaired function and tissue destruction. Numerous anti-diabetic drugs are often prescribed to diabetic patients, to reduce the risk of diabetes through modulation of inflammation. However, those anti-diabetic drugs are often not successful as a result of side effects; therefore, researchers are searching for efficient natural therapeutic targets with less or no side effects. Natural products' derived bioactive molecules have been proven to improve insulin resistance and associated complications through suppression of inflammatory signaling pathways. In this review article, we described the extraction, isolation and identification of bioactive compounds and its molecular mechanisms in the prevention of diabetes associated complications.

On the potential of mass spectrometry-based metabolite profiling approaches to the study of biochemical adaptation in psychrophilic yeast

To move beyond targeted approaches to the biochemical characterization of psychrophilic yeast and provide a more holistic understanding of the chemistry of physiological adaptation of psychrophiles at the molecular level, ultraperformance liquid chromatography combined with simultaneous acquisition of low- and high-collision energy mass spectra (UPLC/MS(e)) was employed for a preliminary comparative analysis of cell extracts of psychrophilic Antarctic yeasts Cryptococcus vishniacii CBS 10616 and Dioszegia cryoxerica CBS 10919 versus the mesophile Saccharomyces cerevisiae 'cry havoc'. A detailed workflow for providing high-confidence preliminary identifications of psychrophilic yeast-specific molecular features is presented. Preliminary identifications of psychrophile-specific features in C. vishniacii and D. cryoxerica determined with the described method include the glycerophospholipids lysophosphatidylcholine 18:2, lysophosphatidylcholine 18:3, lysophosphatidylethanolamine 18:3, and lysophosphatidylethanolamine 18:2. In addition, levels of guanosine diphosphate appear significantly elevated in cell extracts of the psychrophilic yeasts as compared to Saccharomyces cerevisiae. Finally, five psychrophilic yeast-specific peptides have been discovered. All of these are demonstrated to be glycine- and/or proline-rich, a known structural characteristic of many naturally occurring bioactive peptides. The potential of this untargeted metabolite profiling approach as a tool for knowledge discovery and hypothesis generation in the study of biodiversity and microbial adaptation is highlighted.

A mass spectrometry-guided genome mining approach for natural product peptidogenomics

Peptide natural products exhibit broad biological properties and are commonly produced by orthogonal ribosomal and nonribosomal pathways in prokaryotes and eukaryotes. To harvest this large and diverse resource of bioactive molecules, we introduce Natural Product Peptidogenomics (NPP), a new mass spectrometry-guided genome mining method that connects the chemotypes of peptide natural products to their biosynthetic gene clusters by iteratively matching de novo MSⁿ structures to genomics-based structures following current biosynthetic logic. In this study we demonstrate that NPP enabled the rapid characterization of >10 chemically diverse ribosomal and nonribosomal peptide natural products of novel composition from streptomycete bacteria as a proof of concept to begin automating the genome mining process. We show the identification of lantipeptides, lasso peptides, linardins, formylated peptides and lipopeptides, many of which from well-characterized model streptomycetes, highlighting the power of NPP in the discovery of new peptide natural products from even intensely studied organisms.

Differential Antitumor Effects of IgG and IgM Monoclonal Antibodies and Their Synthetic Complementarity-Determining Regions Directed to New Targets of B16F10-Nex2 Melanoma Cells

Malignant melanoma has increased incidence worldwide and causes most skin cancer-related deaths. A few cell surface antigens that can be targets of antitumor immunotherapy have been characterized in melanoma. This is an expanding field because of the ineffectiveness of conventional cancer therapy for the metastatic form of melanoma. In the present work, antimelanoma monoclonal antibodies (mAbs) were raised against B16F10 cells (subclone Nex4, grown in murine serum), with novel specificities and antitumor effects in vitro and in vivo. MAb A4 (IgG2ak) recognizes a surface antigen on B16F10-Nex2 cells identified as protocadherin beta(13). It is cytotoxic in vitro and in vivo to B16F10-Nex2 cells as well as in vitro to human melanoma cell lines. MAb A4M (IgM) strongly reacted with nuclei of permeabilized murine tumor cells, recognizing histone 1. Although it is not cytotoxic in vitro, similarly with mAb A4, mAb A4M significantly reduced the number of lung nodules in mice challenged intravenously with B16F10-Nex2 cells. The V(H) CDR3 peptide from mAb A4 and V(L) CDR1 and CDR2 from mAb A4M showed significant cytotoxic activities in vitro, leading tumor cells to apoptosis. A cyclic peptide representing A4 CDR H3 competed with mAb A4 for binding to melanoma cells. MAb A4M CDRs L1 and L2 in addition to the antitumor effect also inhibited angiogenesis of human umbilical vein endothelial cells in vitro. As shown in the present work, mAbs A4 and A4M and selected CDR peptides are strong candidates to be developed as drugs for antitumor therapy for invasive melanoma.

Antifungal and antitumor models of bioactive protective peptides

Peptides are remarkably reactive molecules produced by a great variety of species and able to display a number of functions in uni-and multicellular organisms as mediators, agonists and regulating substances. Some of them exert cytotoxic effects on cells other than those that produced them, and may have a role in controlling subpopulations and protecting certain species or cell types. Presently, we focus on antifungal and antitumor peptides and discuss a few models in which specific sequences and structures exerted direct inhibitory effects or stimulated a protective immune response. The killer peptide, deduced from an antiidiotypic antibody, with several antimicrobial activities and other Ig-derived peptides with cytotoxic activities including antitumor effects, are models studied in vitro and in vivo. Peptide 10 from gp43 of P. brasiliensis (P10) and the vaccine perspective against paracoccidioidomycosis is another topic illustrating the protective effect in vivo against a pathogenic fungus. The cationic antimicrobial peptides with antitumor activities are mostly reviewed here. Local treatment of murine melanoma by the peptide gomesin is another model studied at the Experimental Oncology Unit of UNIFESP.

Preparation of novel alkylated arginine derivatives suitable for click-cycloaddition chemistry and their incorporation into pseudosubstrate- and bisubstrate-based kinase inhibitors

Efficient strategies for the introduction of arginine residues featuring acetylene or azide moieties in their side chains are described. The substituents are introduced in a way that maintains the basicity of the guanidine moiety. The methodology can be used e.g. for non-invasive labeling of arginine-containing peptides. Its applicability is demonstrated by the introduction of 'click' handles into a Protein Kinase C (PKC) pseudosubstrate peptide, and the subsequent preparation and evaluation of a novel bisubstrate-based inhibitor based on such a peptide.