Medicinal Chemistry Reviews - Online (Discontinued) - Volume 2, Issue 4, 2005

Bifunctional Penicillin-Binding Proteins (PBPs) catalyze bacterial peptidoglycan synthesis; their glycosyltransferase (GT) activity carries out glycan chain polymerization and the transpeptidase domain allows stem peptide crosslinking. The latter domain is the target of β-lactam antibiotics, while the glycosyltransfer region is a potential target for the design of novel antibacterial drugs. This review aims at presenting recent advances related to various aspects of bifunctional PBPs. The coordinated activity between the different PBPs and the peptidoglycan hydrolases has been investigated by genetic and immunofluorescence localization approaches, and the results offer insight onto the cellular functionalities of these essential enzymes. Deletions of all bifunctional PBPs in two Gram-positive organisms did not cause cell death, suggesting the presence of a yet unidentified protein competent for the polymerization of the glycan chains in the absence of the classical GT domain of the PBPs. An important milestone in the study of the GT functionality has been the chemical and enzymatic synthesis of the natural lipid II substrate. This molecule has been employed in detailed study of the GT activity of bifunctional Escherichia coli PBP1b and PBP2a from Streptococcus pneumoniae. Mapping of the interaction between GT domains and inhibitors (moenomycin, vancomycin) and between lipid II and various peptide antibiotics (nisin, mersacidin, ramoplanin) may be useful in the design of new efficient drugs inhibiting peptidoglycan biosynthesis.

Cancer is characterized by cell cycle deregulation, progressive loss of cell differentiation and uncontrolled growth. Since cancer cells are particularly sensitive to oxidative stress, we took advantage of this poor antioxidant status to develop an experimental approach to selectively expose cancer cells to an oxidant insult induced by the association of vitamins C and K3 (CK3). The results we obtained reinforce the major role of oxidative stress as the main mechanism involved in cell killing by CK3, either under in vivo or in vitro conditions. Such an antitumor activity has been attributed to redox cycling of the vitamins and the possible generation of peroxides and other reactive oxygen species. We report herein, on the ability of the association of ascorbate with several quinone derivatives (having different redox potentials) to cause cell death. Finally, we determined that cell death by CK3 is not related to the activation of MAP kinases pathways.

Cysteine proteases are widespread in nature. Their implication in numerous vital processes and pathologies make them highly attractive targets for drug design. The proper functioning and regulation of activity of cysteine proteases is a delicate balance of many factors, one of the most crucial being the protease inhibitors. In this review the basic principles of physiological protease inhibition by protein inhibitors are discussed with the focus on papain-like cathepsins and the caspases, and their inhibitors.

An increase in the frequency of allergic diseases during last several decades has been linked to improved hygienic conditions. This review focuses on a few recent findings in this extensive field. Accumulative data suggest that a spectrum of CD4+T cells, including type 3 T helper cells, T regulatory 1 cells, CD25+T cells, and natural killer T cells, has a crucial role in the regulation of allergic inflammation. Farming environments, found protective against atopic diseases, contain great amounts of microbial compounds, pathogen-associated molecular patterns, which have been shown to induce activation of immunomodulatory genes. These microbe-derived signals are mediated by pattern-recognition receptors which activate different signal transduction pathways in immune and non-myeloid cells. Both pathogens and commensals express these immunomodulatory components. Better understanding of the mechanisms operative in situ may result in new probiotic and other microbe-derived therapies against allergic diseases.

Less than a decade ago, the ability to generate proteins with unnatural modifications was a Herculean task available only to specialty labs. Recent advances make it possible to generate reasonable quantities of protein with unnatural amino acids both in vitro and in vivo . The combination of solid-phase peptide synthesis and enzymatic or chemoselective ligation now permits construction of entirely-synthetic proteins as large as 25 kD. Incorporation of recombinant fragments (expressed protein ligation) allows unnatural modifications near protein termini in proteins of virtually any size. Site-specific modification of small quantities of protein at any position can be achieved using chemically-acylated tRNA. Microelectroporation now extends this method to cells like mammalian neurons, and combination with RNAdisplay makes unnatural proteins compatible with combinatorial methods. Widespread or residue-specific methods of amino acid replacement are especially suitable for the production of biomaterials, and bacteria have been engineered to expand the repertoire of amino acids available for this technique. Excitingly, the wholesale addition of engineered tRNAs and synthetases to bacteria and yeast now makes site-specific incorporation of unnatural amino acids possible in living cells with no chemical intervention. Methods of expanding the genetic code at the nucleic acid level, including 4-base codons and unnatural base pairs, are becoming useful for the addition of multiple amino acids to the genetic code. These recent advances in unnatural protein engineering are reviewed with an eye toward future challenges, including methods of creating nonpeptidic molecules using templated synthesis.

Human telomeres are several kilobases of repeated (TTAGGG)n sequences at the ends of chromosomes, a short fragment of which is lost with each cell division. This shortening serves as a "mitotic clock", limiting the number of divisions which normal somatic cells can undergo. Cells undergoing continuous division need some method of bypassing this clock. One such method is the expression of telomerase, a ribonucleoprotein that rebuilds the lost portion of telomeres. Between 80-95% of tumors are telomerase-positive, including ovarian and hepatocellular carcinoma, neuroblastoma, leukemia/lymphoma, and cancers of the breast, prostate, lung, kidneys and bladder, and many immortalized cell lines. While absent in most normal tissues, it's expressed at higher levels in germline tissues, bone marrow, and lymphocytes. Due to telomerase expression in most tumor cells and its absence in most normal tissues, telomerase inhibitors are being investigated as anticancer agents. This review focuses on non-reverse transcriptase inhibitor, nonoligonucleotide, non-G-quartet interactive agent telomerase inhibitors. These agents include: differentiating agents, kinases and phosphatases, cell cycle and apoptosis regulating agents, immunotherapeutic agents, antibiotics, steroids, bisindole derivatives, and a variety of other compounds, including herbal medical compounds and cyclooxygenase inhibitors. These agents hold great promise for the future treatment of malignancies.

Proteoglycans (PG) are complex macromolecules which consist structurally of a core protein and associated glycosaminoglycan (GAG) chains. The different GAG chains of PG, heparan sulfate/heparin, dermatan/chondroitin sulfate, keratan sulfate are synthesized as polymers of repeating disaccharide units. The structures of GAG chains are highly diverse and confer to them a variety of structures and functions. Without covering PG complexity in structures and roles, the most usual classification for PG is based on their localization: being at the cell membrane or in the extracellular matrix, being intracellular or circulating in the blood. By virtue of the multiplicity of protein binding partners (e.g. growth factors, chemokines), PG have been shown to be involved in the regulation of a large number of pathophysiological processes. They are strongly implicated in the different stages of inflammation from the recruitment of inflammatory cells to the release of mediators of inflammation by infiltrating leukocytes and the turnover of extracellular matrix. The overarching theme of PG in inflammation is the regulation of the inflammatory microenvironment, which has to change continuously and dynamically during the progression of the inflammatory response. These changes include the modulation of the activity of GAG-binding cytokines, growth factors, proteases and protease inhibitors. The interactions of regulatory proteins with GAGs provide much of the focus for GAG-based therapeutic targets and the development of GAG mimetics could have in the near future, clinical applications as modulators of cytokine or enzyme functions in inflammatory diseases.

Amyloid beta (Aβ) protein in Alzheimer's disease and scrapie prion protein (PrPsc) in Scrapie is the key component of amyloid plaques in brain whereas stefin B is an intracellular cysteine proteinase inhibitor, broadly distributed in different tissue and recently reported to form amyloid fibrils in vitro. By reducing the pH to around 4.6, the native conformation of both polypeptides is changed into less ordered, metastable intermediates that are stabilised by formation of the more stable fibrils. In Aβ, the Glu at position 11 was found to be responsible for the conformational change at pH 4.6. Metal ions, including copper and zinc, could also induce conformational changes of Aβ at neutral pH. The acid modified Aβ conformer exhibited protease K resistance, preferential internalisation and accumulation in the human glial cells. In N-terminally truncated PrP90-231, spanning PrP residues 94-112 and the central region 146-154 incorporating Glu152 was identified as a significant participant for the conformational changes in acidic pH. In stefin B, reducing the pH to pH 3.3 results in another intermediate of the molten-globule type which also leads to amyloid fibril formation. Multiple sequence alignment revealed distinct similarities of Ab (1-42) peptide, stefin B (13 to 61 residues) and prion fragment (90 to 144 residues).