Current Protein and Peptide Science - Volume 10, Issue 4, 2009

Proteases constitute one of the primary targets in drug discovery. In the present review, we focus on extracellular proteases (ECPs) because of their differential expression in many pathophysiological processes, including cancer, cardiovascular conditions, and inflammatory, pulmonary, and periodontal diseases. Many new ECP inhibitors are currently under clinical investigation and a significant increase in new therapies based on protease inhibition can be expected in the coming years. In addition to directly blocking the activity of a targeted protease, one can take advantage of differential expression in disease states to selectively deliver therapeutic or imaging agents. Recent studies in targeted drug development for the metalloproteases (matrix metalloproteinases, adamalysins, pappalysins, neprilysin, angiotensin-converting enzyme, metallocarboxypeptidases, and glutamate carboxypeptidase II), serine proteases (elastase, coagulation factors, tissue/urokinase plasminogen activator system, kallikreins, tryptase, dipeptidyl peptidase IV) and cysteine proteases (cathepsin B) are discussed herein.

Milk and colostrum is a rich source of proteins/peptides which have crucial roles in both neonates and adults. Milk bioactive proteins and peptides are potential health-enhancing nutraceuticals for food. Many bioactive peptides/ proteins may be used as nutraceuticals, for example, in the treatment of cancer, asthma, diarrhea, hypertension, thrombosis, dental diseases, as well as mineral malabsorption, and immunodeficiency. The following components of milk are of particular interest in the recent years: 1) Lactoferrin [Lf] has antibacterial, antifungal, antiviral, antiparasite and antitumor activities and accelerates immunomodulatory properties. Lf is a potent inhibitor for several enveloped and naked viruses, such as rotavirus, enterovirus and adenovirus. Lf is resistant to tryptic digestion and breast-fed infants excrete high levels of faecal Lf, so that its effect on viruses replicating in the gastrointestinal tract is of great interest. 2) Casein has been protective in experimental bacteremia by eliciting myelopoiesis. Casein hydrolyzates were also protective in diabetic animals, reduced the tumor growth and diminished colicky symptoms in infants. 3) A Proline rich polypeptide [PRP] revealed variety of immunotropic functions, including promotion of Tcell activation and inhibition of autoimmune disorders such as multiple sclerosis. 4) α-Lactalbumin [LA] demonstrates antiviral, antitumor and anti-stress properties. 5) Lactoperoxidase shows antibacterial properties. 6) Lysozyme is effective in treatment of periodentitis and prevention of tooth decay. Taken together, milk-derived proteins and peptides are bio-available and safe for the prevention and treatment of various disorders in humans and may play a complementary [natural agents] rather than a substitutional role to the toxic synthetic pharmacological drugs.

Amphitrophic proteins are soluble, globular proteins that may - under certain conditions - interact reversibly with a plasma membrane. How this apparent duality in the properties of a protein is achieved has been a relatively littlestudied subject until recently. In this review we aim to summarize the current knowledge regarding some important amphitrophic systems in which the interaction with the membrane does not require post-translational functional groups, but is an intrinsic property of the protein. We discuss mechanisms and driving forces involved in membrane binding in the context of two related concepts in protein folding and function that appear to have implications for understanding the association of proteins with membranes; first, the existence of some proteins with low-energy barrier heights for protein folding. Low folding barriers and the ability of proteins to form stable molten globule states are rationales that can explain how a protein can gain access to an ensemble (or continuum) of non-native conformations that are competent membrane binders. Second, the focus on order-disorder and disorder-order transitions to explain protein function, a concept which has been mainly developed within the novel protein trinity paradigm. Here, protein function can arise from any of three thermodynamic states: a solid, crystal-like state; a dense fluid state; and an extended disordered state. Together these concepts aid to understand amphitrophic mechanism and to unify interpretations of protein behaviour with respect to the degree of (un)unfolding of the membrane-bound proteins.

Metallothioneins (MTs) are low molecular, cysteine-rich proteins that have naturally-occurring Zn2+ in both clusters. They may serve as a reservoir of metals for synthesis of apoenzymes and zinc-finger transcription regulators. MTs are also involved with several important proteins e.g. p53, NF-κB, PKCl, and GTPase Rab3A. New biological roles for these proteins have been identified including those needed in the carcinogenic process. However, their use as a predictive marker remains controversial. Several reports have disclosed MTs expression as a prognostic factor for tumor progression and drug resistance in a variety of malignancies particularly breast, prostatic, ovarial, head and neck, non-small cell lung cancer, melanoma, and soft tissue sarcoma. The role of MTs as a tumor disease marker or as a cause of resistance in cancer treatment is reviewed and discussed. Moreover, we describe some analytical methods that were developed to detect MTs.

Fluorescence spectroscopy methods have been proved to be powerful tools for the quantitative investigation of homologous and heterologous interactions, rotational and translational diffusion, and structural dynamics of biological molecules in crowded media. In addition to their high sensitivity, these methods present the advantage that the selective fluorescent labeling of the biomolecules under study allows distinguishing them from the background species. Moreover, the recent development of biological applications of single molecule fluorescence micro-spectroscopy methods has opened the possibility of performing quantitative determinations inside cells. In the last decades, theoretical and experimental studies have demonstrated the possible influence of the high concentration of macromolecules within living systems, on the thermodynamics and kinetics of biological reactions. Therefore, there is a growing interest in quantitatively evaluating the interactions involving biomolecules in the natural environment in which they occur. Since this is not always feasible, experiments conducted in model crowded conditions, resembling physiological media, may contribute to reduce the gap between traditional in vitro and in vivo experiments. In this review we will discuss the application of some fluorescence spectroscopy approaches, for the identification and quantification of biological macromolecules and their functional interactions in model crowded conditions.

Mammalian cells are prone to tumorigenesis when suffering the genotoxic stresses, and the existence of the tumor suppressors validly decrease this possibility. Gadd45α is one of the growth arrest and DNA damage-inducible (Gadd) 45 gene family members and serves as a stress sensor and tumor suppressor under most stress conditions, which is evidenced by cell cycle arrest, DNA repair, senescence or apoptosis triggered by induction of GADD45α expression. However, some recent reports have challenged this notion by demonstrating the correlation of GADD45α expression to cell survival and even progression of certain tumor cells. Therefore, GADD45?? seems to exert multiple roles in stress signaling and tumor development. Elucidation of the related mechanisms will be helpful for the establishment of novel tumor therapeutic strategy targeting GADD45α.