Current Protein and Peptide Science - Volume 14, Issue 7, 2013

Antimicrobial peptides (AMPs) have been isolated from a wide variety of organisms that include microorganisms, plants, insects, frogs and mammals. As part of the innate immune system expressed in many tissues, AMPs are able to provide protection against invasion of foreign microorganisms and exhibit a broad spectrum of activity against bacteria, fungi and/or virus. Non-AMPs cell-penetrating peptides have been used as carriers for overcoming the membrane barrier and helping in the delivery of various molecules into the cell. Physicochemical peptide-lipid interactions studies can provide us with reliable molecular information about microbe defense response, including the elucidation of the prevailing mechanisms of its action, such as the barrel-stave, toroidal pore, carpet and detergent-like models. In this paper, we present an overview of the peptide-lipid mechanisms of interaction as well as discuss alternative techniques that could help to elucidate the peptides functionality. Quartz crystal microbalance (QCM), surface plasmon resonance (SPR) spectroscopy and electrochemical impedance spectroscopy (EIS) are useful techniques to investigate in details of the peptide-membrane interaction. The techniques here discussed could also offer specific and low-cost methods that can to shed some light over the different modes of action of AMPs, contributing to the development of drugs against infectious diseases.

Numerous peptides are available on the market as therapeutic drugs for regulating tumor growth, microorganism proliferation, immune response and/or metabolic disorders. Peptides are produced either by chemical synthesis or heterologous expression. Independent of the method chosen, there are challenges to transferring its production from the bench (∼mg/L) to the industrial (∼g/L) scale. Thus, the main scale-up pitfalls for the two methods of peptide production are reviewed here, including the advantages of each. Moreover, there will be a special focus on the main challenges for large-scale, heterologous production systems. Peptides that are currently available on the market are also described with an emphasis on how their process optimization has been designed in order to develop a cost-effective product.

Recombinant DNA technology has allowed the ectopic production of proteins and peptides of different organisms leading to biopharmaceutical production in large cultures of bacterial, yeasts and mammalian cells. Otherwise, the expression of recombinant proteins and peptides in plants is an attractive alternative presenting several advantages over the commonly used expression systems including reduced production costs, easy scale-up and reduced risks of pathogen contamination. Different types of proteins and peptides have been expressed in plants, including antibodies, antigens, and proteins and peptides of medical, veterinary and industrial applications. However, apart from providing a proof of concept, the use of plants as platforms for heterologous protein and peptide production still depends on key steps towards optimization including the enhancement of expression levels, manipulation of post-transcriptional modifications and improvements in purification methods. In this review, strategies to increase heterologous protein and peptide stability and accumulation are discussed, focusing on the expression of peptides through the use of gene fusions.

Nowadays, peptide based disease prevention is an important topic in biomedical science, which may radically change the traditional use of biomaterials and improve the life quality. Self-assembled nanostructured peptides have been receiving extreme attention in the drug delivery field due their high biocompatibility levels, better loading capacity, extended circulation and localization in required target site. This article focuses on the composition and synthesis of different forms of self-assembled peptide nanostructures as nanotubes, nanofibers, nanoparticles, nanotapes and nanogels. The most important properties for their self assembled mechanism and their biomedical applications are also discussed. Various potential applications of nanostructures peptide could be developed designed for therapeutic agent’s delivery, biosensors, anticancerous and antimicrobial activities.

Biotechnology and nanotechnology are fields of science that can be applied together to solve a variety of biological issues. In the case of human health, biotechnology attempts to improve advances on the therapy against several diseases. Therapeutic peptides and proteins are promissory molecules for developing new medicines. Gene transfection and RNA interference have been considered important approaches for modern therapy to treat cancer and viral infections. However, because of their instability, these molecules alone cannot be used for in vivo application, since they are easily degraded or presenting a poor efficiency. Nanotechnology can contribute by the development of nanostructured delivery systems to increase the stability and potency of these molecules. Studies involving polymeric and magnetic nanoparticles, dendrimers, and carbon nanotubes have demonstrated a possibility to use these systems as vectors instead of the conventional viral ones, which present adverse effects, such as recombination and immunogenicity. This review presents some possibilities and strategies to efficiently delivery peptides, proteins, gene and RNA interference using nanotechnology approach.

Antimicrobial peptides are distributed in all forms of life presenting activity against bacteria, fungi, viruses, parasites and cancer. In spite of the tremendous potential of these molecules, very few of them have been successfully developed into therapeutics. The major problems associated with this new class of antimicrobials are molecule stability, toxicity in host cells and production cost. A novel strategy to overcome these obstacles is conjugation to nanomaterials. Magnetic nanoparticles have been widely studied in biomedicine due to their physicochemical properties. The conjugation of antimicrobial peptides to magnetic nanoparticles could combine the best properties of both, generating an improved antimicrobial nanoparticle. Here we provide an overview and discuss the potential application of magnetic nanoparticles conjugated to antimicrobial peptides in overcoming diseases.

Antimicrobial peptides (AMPs) are evolutionarily conserved components of the innate immune defense system of many living organisms varying from prokaryotes to eukaryotes, including humans. Due to their broad-spectrum activity and low level of induced resistance, these short aminoacid sequences represent a novel class of potential antimicrobial agents. Besides the development of anti-bacterial drugs, AMPs constitute ideal molecular models for the design of molecules with wide-ranging nanomedical applications, such as anti-tumorigenic agents and pharmacological tools to cure channelopaties. Several techniques are currently used to shed light on the mechanisms of action of AMPs, ranging from the characterization of the interaction between peptides and biomimetic membranes and/or intracellular targets, to the study of AMPs effects on pathogens, living cells and tissues. Comprehensive and multiscale studies are crucial to design new AMPs and to identify molecules that can boost their activity. In this minireview we summarize the most recent achievements in AMP-characterization, with a special emphasis on the integration of biophysical approaches, which can synergistically help to bridge the gap between in vitro and ex vivo investigations.

Growing evidence has shown that the proforms of several neurotrophins, e.g., nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin3 (NT3) can be synthesized, secreted from neurons or glial cells and function actively in mammalian nervous system. By the intracellular and extracellular enzymatic cleavage processing, mature neurotrophins are generated and exert their functions in the developing, physiological and pathological activities. While mature neurotrophins exhibit neuroprotective roles via tyrosine kinase receptors (TrkA, TrkB and TrkC), the proforms of neurotrophins show totally-different biological effects that may induce apoptotic cell death of neurons by triggering p75NTR-sortilin signaling cascades. In addition, another key neurotrophic factor named glial-derived neurotrophic factor (GDNF) also appears to be a product generated from proGDNF, and its cleavage and potential biological function of proGDNF remains an unrevealed problem. Obviously, accumulating studies indicated that the exact or timely cleavage processing should be essential for the functional switch from proneurotrophins to mature neurotrophins, while dysfunction in the enzymatic cleavage, aberrant extracellular release, and abnormal subunit organization of binding receptors might be also crucially involved in neurodegeneration of the central neurons, pathogenesis, and even disease progression of various neurodegenerative diseases in human beings.

The dystroglycan (DG) adhesion complex is formed by the peripheral α-DG and the transmembrane β-DG, both originating from the same precursor. α-DG plays a crucial role for tissue stability since it binds with high affinity a variety of proteins and proteoglycans in many different cell types. One common molecular feature of most of the α-DG ligands is the presence of laminin globular (LG) domains that are likely to interact with some of the carbohydrates protruding from the mucin-like region of α-DG. Every tissue is supposed to produce a specific α-DG harboring a particular sugar moiety that will enable it to bind a specific ligand, but often several α-DG ligands are co-expressed within the same tissue. It is therefore very important to assess all these different interactions, ultimately measuring the affinity constants (KDS) underlying them. Herein, we present an updated list of α-DG interactors, including non LG-domains containing ligands, offering both a historic perspective on the original contributions made by several laboratories and an update on the different techniques used and the KD values obtained so far. For the cure of some muscular dystrophies, the reinstatement of a prominent affinity between α-DG and one of its vicarious ligands is becoming an increasingly popular choice for strengthening the basement membrane-tissue connection. An update on the current available information about α- DG′s multiple, and often “concomitant“ affinities, may be of interest for those wishing to better direct their molecular therapy approaches. A final paragraph is dedicated to comment on the evidence that an increase in affinity is not always advantageous.

Receptor tyrosine kinases (RTKs) are cell surface receptors that transmit extracellular signals to the interior of the cell activating multiple signaling cascades: the binding of specific extracellular ligands activates RTKs which act as a scaffold at plasma membrane level for the recruitment and activation of several signaling molecules. A paradigm shift emerged when an alternative direct signaling pathway was discovered: RTKs may move from cell surface to nucleus where they transduce the signals in a direct way. More recently, evidence has accumulated that RTKs may also translocate to mitochondria and regulate their functions, i.e., by altering tyrosine phosphorylation of specific mitochondrial proteins. This latter emerging pathway is here reviewed and discussed.