Current Protein and Peptide Science - Volume 5, Issue 6, 2004

The practical development of modern vaccines has been greatly advanced by the availability of synthetic antigens. The use of such synthetic antigens might be more acceptable for human therapy since synthetic peptides do not have any of the potential dangers associated with the induction of an infection by recombinant viruses. However, synthetic peptides alone are often not immunogenic enough, and a strong immunoadjuvant is usually employed for their elaboration. Unfortunately, only a few adjuvants used in experimental models are allowed for use in human beings. In this regard, different presentations of synthetic peptides such as incorporation into liposomes, modification of the lipophilic properties by means of a covalently coupled fatty acid moiety and the synthesis of larger constructs such as multiple antigenic peptides (MAP) have been demonstrated to yield efficient immunological reagents for the amplification in the analysis and induction of immune responses to a variety of infectious agents. This review outlines recent research on synthetic peptide immunology. The development of a MAP with a built-in adjuvant is highlighted as a robust method for vaccine design.

In recent years, there has been increasing interest in de novo design and construction of novel synthetic peptides that mimic protein secondary structures, i.e., turns, helices and sheets. The unique structural influences exerted by unsubstituted, non-coded, non-chiral βamino acid, i.e., βalanine (βAla; 3- or beta- aminopropionic acid) on peptide backbone, when inserted into peptide chain comprised α-amino acids, offer an excellent opportunity to design and construct diverse well-defined three-dimensional structures. Our current understanding of folding-unfolding behavior of the βAla residues relies primarily from an examination of conformational preferences of a large number of short cyclicas well as acyclic βAla containing peptides investigated using single crystal X-ray diffraction analysis. In addition, theoretical conformational energy calculations and different spectroscopic techniques: 1H NMR, FT-IR and CD, have also been employed although, to a lesser extent. The obtainable results tend to reveal overwhelming preferences of the βAla moiety for the folded gauche (m ∼ ±65±10 ) conformation in cyclic- and for an extended trans (m ∼ ±165±10 ) as well as gauche (m ∼ ±65±10 ) orientations in acyclic βAla containing peptides. The results also indicate that in short linear βAla containing peptides, the specific influence of selective neighboring side-chain substituents e.g. linear- or cyclic symmetrically Ca,a-disubstituted glycines and other conformational constraints, may be significant in controlling the overall folded-unfolded topographical features across the two methylene units (-CbH2-CaH2-) of the βAla residue. Taking into consideration the wide occurrence of βAla moiety in animal and plant kingdoms and the remarkable structural versatility of the peptides incorporating βAla residue(s), together with appreciable resistance towards enzymatic degradation, hold strong promise for biophysicists and biochemists not only to design molecules that fold to mimic protein secondary structures but also to develop potent peptide analogs and peptidomimetics displaying unique pharmaceutical properties.

The neuropeptides, as well as their respective receptors, are widely distributed throughout the mammalian central nervous system. During learning and memory processes, besides structural synaptic remodeling, changes are observed at molecular and metabolic levels with the alterations in neurotransmitter and neuropeptide synthesis and release. While there is consensus that brain cholinergic neurotransmission plays a critical role in the processes related to learning and memory, it is also well known that these functions are influenced by a tremendous number of neuropeptides and non-peptide molecules. Arginine vasopressin (AVP), oxytocin, angiotensin II, insulin, growth factors, serotonin (5- HT), melanin concentrating hormone, histamine, bombesin and gastrin-releasing peptide (GRP), glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK), dopamine, corticotropin releasing factor (CRF) have modulatory effects on learning and memory. Among these peptides CCK, 5-HT and CRF play strategic roles in the modulation of memory processes under stressful conditions. CRF is accepted as the main neuropeptide involved in both physical and emotional stress, with a protective role during stress, possibly through the activation of the hypothalamo-pitiuitary (HPA) axis. The peptide CCK has been proposed to facilitate memory processing and CCK-like immunoreactivity in the hypothalamus was observed upon stress exposure, suggesting that CCK may participate in the central control of stress response and stress-induced memory dysfunction. On the other hand, 5-HT appears to play a role in behaviors that involve a high cognitive demand and stress exposure activates serotonergic systems in a variety of brain regions. The physiological role and therapeutic efficacy of various neuropeptides and the impact of stress exposure in the acquisition and consolidation of memory will be reviewed thoroughly.

Interferon-α (IFNα) is a recombinant protein widely used in the therapy of several neoplasms such as myeloma, renal cell carcinoma, epidermoid cervical and head and neck tumours and melanoma. IFNα, the first cytokine to be produced by recombinant DNA technology, has emerged as an important regulator of cancer cell growth and differentiation, affecting cellular communication and signal transduction pathways. However, the way by which tumour cell growth is directly suppressed by IFNα is not well known. Wide evidence exists on the possibility that cancer cells undergo apoptosis after the exposure to the cytokine. Here we will review the consolidate Signal transducer and activator of transcription (STAT)-dependent mechanism of action of IFNα and the supposed mechanism of apoptosis induction by IFNα. We will discuss data obtained by us and others on the triggering of the stress-dependent kinase pathway and on the modulation of protein synthesis machinery induced by IFNα and their correlations with the apoptotic process. Until today, inconsistent data have been obtained regarding the clinical effectiveness of IFNα in the therapy of solid tumours. In fact, the benefit of IFNα treatment is limited to some neoplasms while others are completely or partially resistant. The mechanisms of tumour resistance to IFNα have been studied in vitro. The alteration of JAK- Signal transducer and activator of transcription components of the IFNα-induced signalling, can be indeed a mechanism of resistance to IFN and cross talks between IFNα and survival signals has been also described. However, we have recently described a reactive mechanism of protection of tumour cells from the apoptosis induced by IFNα dependent on the epidermal growth factor (EGF)-mediated Ras / extracellular signal regulated kinase (Erk) signalling. The involvement of the Ras->Erk pathway in the protection of tumour cells from the apoptosis induced by IFNα is further demonstrated by both Ras inactivation by RASN17 transfection and mitogen extracellular signal regulated kinase 1 (Mek-1) inhibition by exposure to PD098059. These data strongly suggest that the specific disruption of the latter could be a useful approach to potentiate the antitumour activity of IFNα against human tumours based on the new mechanistic insights achieved in the last years.

Combinatorial chemistry and biology have become popular methods for the identification of bio-active molecules in drug discovery. A widely used technique in combinatorial biology is “phage display”, by which peptides, antibody fragments and enzymes are displayed on the surface of bacteriophages, and can be selected by simple procedures of biopanning. The construction of phage libraries of peptides or antibody fragments provides a huge source of ligands and bio-active molecules that can be isolated from the library without laborious studies on antigen characteristics and prediction of ligand structure. This “irrational” approach for the construction of new drugs is extremely rapid and is now used by thousands of laboratories world-wide. The bottleneck in this procedure is the availability of large reliable libraries that can be used repeatedly over the years without loss of ligand expression and diversity. Construction of personalized libraries is therefore important for public and private laboratories engaged in the isolation of specific molecules for therapeutic or diagnostic use. Here we report the general strategies for constructing large phage peptide and antibody libraries, based on the experience of researchers who built the world's most widely used libraries. Particular attention is paid to advanced strategies for the construction, preservation and panning.

Brain asymmetry is understood as an anatomical, functional or neurochemical difference between the two hemispheres. It is not a static but rather a dynamic phenomenon in which both environmental and endogenous factors act as modulators. Aging modifies brain asymmetry, and an imbalance in specific asymmetries characterizes some brain disorders such as schizophrenia, depression, infantile autism or Alzheimer's disease. However, it is not clear whether these changes are a cause or a consequence of these disorders. Although this phenomenon has been extensively studied, its functional significance is not yet clear, and the neurochemical basis underlying anatomical or functional asymmetries in the brain is still poorly understood. In recent decades intensive research on the behaviour of neuropeptides has revealed asymmetries in their distribution in the brain, and there is evidence that the lateralized patterns of distribution are involved in the regulatory control of some neuropeptidase activities. Therefore, if these enzymatic activities are distributed asymmetrically, their endogenous substrates would presumably be affected in an asymmetrical way, as would the functions they are involved in. Here we review the most significant literature regarding human and animal brain asymmetry involving neuropeptides such as corticotropin-releasing hormone, cholecystokinin, luteinizing hormonereleasing hormone, thyrotropin-releasing hormone and angiotensin II, as well as their neuropeptidases.

The review presents three hypotheses concerning the amino acid complementarity: 1) the Mekler-Blalock antisense hypothesis; 2) the Root-Bernstein approach based on stereochemical complementarity of amino acids and antiamino acids coded by anticodons read in parallel with the coding DNA strand; 3) Siemion hypothesis resulting from the periodicity of the genetic code. The current state of knowledge as well as the results of the implementations of these hypotheses are compared. A special attention is given to Root-Bernstein and Siemion hypotheses, which differ in only few points of the complementarity prediction. We describe methods of investigation of peptide - antipeptide pairing, including circular dichroism, mass spectrometry, affinity chromatography and other techniques. The biological applications of complementarity principle are considered, such as search for bioeffector - bioreceptor interaction systems, the influence of peptide - antipeptide pairing on the activity of peptide hormones, and the application of antipeptides in immunochemistry. The possible role of amino acid - anti-amino acid interactions in the formation of the spatial structures of peptides, proteins and protein complexes is discussed. Such problems as the pairing preferences of protein - protein interfaces, the role of the pairing in the creation of disulfide bonds and the possible appearance of such interactions in β-structure are also examined. The main intention of the paper is to bring the complementarity problem to the attention of the scientific community, as a possible tool in proteomics, molecular design and molecular recognition.