Current Protein and Peptide Science - Volume 14, Issue 8, 2013

The increasing frequency of multidrug-resistant bacteria and a recent slowing in the development of new antimicrobial agents place mankind in a state of emergency with regard to the threat of new bacterial infections. Antibacterial peptides (AMPs) are considered an important class of molecules to develop against bacteria. AMPs have been known for many years but very few have yet been extensively used in clinical practice, mainly because of their general toxicity and manufacturing cost. Now, thanks to new technologies for screening and development, interest in these molecules has grown. Many new AMPs have been discovered and some are under evaluation for the development of new antibacterial therapeutics. Here we review the major AMPs currently used in clinical practice and others in the phase of preclinical and clinical development.

Phospholipases C beta (PLC-βs) are essential components of the signal transduction of metazoans. They catalyze the production of the second messengers inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) from the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PIP2). These enzymes are activated by G-protein-coupled receptors (GPCRs) through the interaction with the alpha subunit of heterotrimeric G-proteins belonging to the Gq family (Gαq), the Gβγ subunits released by the inhibitory G-protein (Gi) and Ca2+ ions. Here we review current structural insights on these important proteins, with a particular focus on the most structurally characterized isoform (PLC-β3) and the activation mechanism operated by Gαq. We propose, following the lead of recent studies, that a tight combination of experiments and molecular simulations are instrumental in further enlightening the structure/function understanding of PLC-βs.

HIV-1, the agent responsible for AIDS, belongs to the retrovirus family. Assembly of the immature HIV-1 capsid occurs through the controlled polymerization of the Gag polyprotein, which is transported to the plasma membrane of infected cells, where morphogenesis of the immature, non-infectious virion occurs. Moreover, the mature capsid of HIV-1 is formed by the assembly of copies of the capsid protein (CA), which results, among other proteins, from cleavage of Gag. The C-terminal domain of CA (CTD) can homodimerize, and most of the dimerization interface is formed by a single α-helix from each monomer. Assembly of the HIV-1 capsid critically depends on CA-CA interactions, including CTD interaction with itself and with the N-terminal domain of CA (NTD). This review will report on recent advances for the search of small organic compounds and peptides that have been designed in the last four years to hamper CA assembly. Most of the molecules have been proved to interact with CA; such molecules aim to disrupt and/or alter the oligomerization capability of CTD and/or NTD.

Impaired insulin sensitivity, namely insulin resistance, is a metabolic and functional disorder that is often associated with the type 2 diabetes mellitus and/or obesity. Recent studies have provided compelling clues that the neuropeptide galanin is closely related to insulin sensitivity in skeletal muscle and adipose tissue of rats. This peptide may regulate glucose homeostasis and carbohydrate metabolism in peripheral tissues, as well as accelerate the translocation of glucose transporter 4 to the plasma membrane of various insulin-sensitive cells to reduce insulin resistance. Galanin plays a crucial role in inhibiting insulin secretion from pancreatic β cells to prevent hyperinsulinemia, which is a characteristic of type 2 diabetes mellitus. This review provides a comprehensive aggregation of the current literature available, bringing together data gleaned from our recent studies highlighting the role of galanin in regulating insulin sensitivity. This comprehensive role played by galanin and its relative agents in regulating insulin secretion and insulin sensitivity provides a new insight into the influence of this neuropeptides on the prevention and treatment of type 2 diabetes mellitus.

Autism and autism spectrum disorders (ASDs) are heterogeneous, severe neurodevelopmental pathologies. These enigmatic conditions have their origins in the interaction of multiple genes and environmental factors. Dysfunctions in social interactions and communication skills, restricted interests, repetitive and stereotypic verbal and non-verbal behaviours are the main core symptoms. Several biochemical processes are associated with ASDs: oxidative stress; endoplasmic reticulum stress; decreased methylation capacity; limited production of glutathione; mitochondrial dysfunction; intestinal impaired permeability and dysbiosis; increased toxic metal burden; immune dysregulation. Current available treatments for ASDs can be divided into behavioural, nutritional and medical approaches, although no defined standard approach exists. Dietary bioactive proteins and peptides show potential for application as health-promoting agents. Nowadays, increasing studies highlight a key role of bioactive proteins and peptides in ASDs. This review will focus on the state-of-the-art regarding the involvement of dietary bioactive proteins and peptides in ASDs. Identification of novel therapeutic targets for ASD management will be also discussed.

The largest human gene is represented by the X-chromosomal dystrophin gene of 2.4 million bases, which encodes for the membrane cytoskeletal protein dystrophin. The dystrophin isoform Dp427 has a subsarcolemmal location and forms a supramolecular membrane assembly with a variety of glycoproteins. In healthy muscle fibres, dystrophin acts as an actin-binding protein that links the cytoskeleton via the α/β-dystroglycan complex to the extracellular matrix protein laminin. This trans-sarcolemmal complex is believed to stabilize the muscle surface and thus prevents membrane rupturing during excitation-contraction-relaxation cycles. In the highly progressive muscle wasting disease Duchenne muscular dystrophy, the primary deficiency in dystrophin causes a drastic reduction in dystrophin-associated glycoproteins, which renders muscle fibres more susceptible to necrosis. Following the biochemical and cell biological characterization of the dystrophin-glycoprotein complex, several mass spectrometry-based proteomic studies have investigated global changes in dystrophin-deficient muscle tissues. This review briefly outlines the basic domain structure of Dp427 and the composition of the dystrophin-associated glycoprotein complex from skeletal muscle. A detailed discussion of recent proteomic analyses of the purified dystrophin-glycoprotein complex is included, as well as a summary of mass spectrometric surveys of dystrophic specimens. The study of these new areas of muscle proteomics tends to improve our understanding of the normal function of dystrophin in contractile fibres and better define the molecular mechanism of X-linked muscular dystrophy.

Antimicrobial peptides (AMPs) are found as important components of the innate immune system (host defense) of all invertebrates. These peptides can be constitutively expressed or induced in response to microbial infections. Indeed, they vary in their amino acid sequences, potency and antimicrobial activity spectra. The smaller AMPs act greatly by disrupting the structure or function of microbial cell membranes. Here, the insect innate immune system with emphasis on inducible antimicrobial peptide properties against microbial invaders has been discussed.

The renin-angiotensin system (RAS) consists of a complex enzyme-peptide system, which, besides from functioning as a circulating endocrine system, is also intrinsic in many organs and tissues, including the brain. Although the RAS generates a family of biological active peptides, angiotensin II (Ang II) is still considered one of its main mediators and effectors. Ang II produces many well defined and potent effects through AT1 and AT2 receptors and its physiological applications are yet expanding. Recently, it has been proposed that Ang II, acting both centrally and peripherally, interferes on exercise performance due to its influence on multiple functions within the organism. This hypothesis is also supported by evidences reporting an increased frequency of the ACE I allele among elite athletes, suggesting that this is a genetic factor that influences physical performance. The fatigue resulting from physical exercise is a multifactorial phenomenon that comprises the interaction between physiological factors of peripheral and/or central origin. To that extent, the Ang II-mediated events on factors that affect exercise performance such as cardiovascular, metabolic and thermoregulatory adjustments as well as cerebral metabolism and neurohumoral or neurotransmitter turnover, implicate the peptide in the genesis of exercise-induced fatigue. This mini-review focuses on how exercise-induced physiological adjustments are influenced by Ang II within the central nervous system and how these effects may limit athletic performance.

Protein folding in vivo is extremely intricate and challenging to examine or predict because the conformational changes, including folding, misfolding, and aggregation, are largely influenced by the cellular environment. Traditionally, cellular protein folding has been considered predominantly in the context of the Anfinsen postulate and molecular chaperones. However, accumulating evidence reveals that these models have limitations. In this review we revisit these models, and discuss co-translational folding, binding partner-mediated folding, and RNA-mediated folding as alternative or supplementary folding helpers. In addition, we discuss the folding helper systems mediated by macromolecules (e.g., ribosomes, membranes, and prefolded domains in multidomain proteins) that are tightly linked to newly synthesized polypeptides during protein biogenesis. These cis-acting folding helper systems, conceptually different from the trans-acting molecular chaperones, could play a crucial role in protein folding in vivo. Importantly, there is increasing evidence that the surface charges and excluded volume of macromolecules are important factors for stabilizing their connected polypeptides against aggregation. This stabilizing mechanism suggests that macromolecules including RNAs and proteins, let alone molecular chaperones, have an intrinsic ability to exert chaperoning function on their connected polypeptides independent of the linkage type between them. As an effective way to overcome the adverse effect of macromolecular crowding on protein folding, here we suggest that nascent polypeptide chains utilize the crowded environment in favor of productive folding by interacting with macromolecules.

Gene-encoded peptide antibiotics represent fascinating molecules for the development of new antimicrobials with a new mode of action: and one of the richest sources is amphibian skin. In particular, the skin of the fire-bellied toad Bombina genus contains mildly cationic antimicrobial peptides (AMPs), named bombinins H, with attractive properties. Indeed, some members of this peptide family coexist in skin secretions as isomers in which a single D-amino acid (alloisoleucine or leucine) is incorporated as a result of a post-translational modification of the respective gene-encoded Lamino acid. Here, a brief overview of the genes coding for these peptides, their spectrum of antimicrobial activities, mechanism of action and interactions with biological or model membranes is reported. Remarkably, a single D-amino acid substitution represents a unique approach developed by Nature not only to modulate the peptide stability in vivo, but also to confer the all-L peptide and its diastereomer distinctive biological features. Overall, such findings should assist in the generation of new peptide-based anti-infective agents, which are urgently needed because of the growing emergence of microbial strains resistant to conventional antimicrobials.