The ability of 2-deoxy-d-glucose (2-DG) to interfere with d-glucose metabolism demonstrates that nutrient and energy deprivation is an efficient tool to suppress cancer cell growth and survival. Acting as a d-glucose mimic, 2-DG inhibits glycolysis due to formation and intracellular accumulation of 2-deoxy-d-glucose-6-phosphate (2-DG6P), inhibiting the function of hexokinase and glucose-6-phosphate isomerase, and inducing cell death. In addition to glycolysis inhibition, other molecular processes are also affected by 2-DG. Attempts to improve 2-DG's drug-like properties, its role as a potential adjuvant for other chemotherapeutics, and novel 2-DG analogs as promising new anticancer agents are discussed in this review.using gluconeogenesis [5]. The hydrophilic nature of glucose requires specific glucose transporter proteins (GLUTs) to facilitate cellular uptake [6]. Higher glucose utilization by tumor cells requires overexpression of GLUT transporters to increase glucose uptake over 20-30 fold as compared to normal cells [7,8].Once inside the cell, glucose enters a cycle of changes to release energy in the form of ATP. Normal cells with access to oxygen utilize glycolysis to metabolize glucose into two molecules of pyruvate and form two molecules of ATP. The pyruvate is further oxidized in the mitochondria to acetyl-CoA via the pyruvate dehydrogenase complex. Acetyl-CoA then enters the Krebs cycle, in which it is oxidized into 2 molecules of CO 2 . The electrons derived from this process are used to create three molecules of NADH and one molecule of FADH 2 . These electron carrier molecules are reoxidized through the oxidoreductive systems of the respiratory chain, which drives ATP formation from ADP and inorganic phosphate (P i ) [9]. As a result of oxidative phosphorylation, 30 ATP molecules are generated from one molecule of glucose versus a net of 2 from glycolysis [9,10]. Oxygen is vitally important for this process as the final electron acceptor, allowing complete oxidation of glucose. In the case of insufficient oxygen concentrations, for example in skeletal muscle during periods of intense exertion, cells fall back on glycolysis, an ancient metabolic pathway evolved before the accumulation of significant atmospheric oxygen. Pyruvate, the end product of glycolysis, is reduced to lactate via lactic acid fermentation, cycling NADH back to NAD + [11]. The comparison of glucose metabolic pathways is presented in Figure 1.
The conserved decapping enzyme Dcp2 recognizes and removes the 5′ eukaryotic cap from mRNA transcripts in a critical step of many cellular RNA decay pathways. Dcp2 is a dynamic enzyme that functions in concert with the essential activator Dcp1 and a diverse set of coactivators to selectively and efficiently decap target mRNAs in the cell. Here we present a 2.84 Å crystal structure of K. lactis Dcp1–Dcp2 in complex with coactivators Edc1 and Edc3, and with substrate analog bound to the Dcp2 active site. Our structure shows how Dcp2 recognizes cap substrate in the catalytically active conformation of the enzyme, and how coactivator Edc1 forms a three-way interface that bridges the domains of Dcp2 to consolidate the active conformation. Kinetic data reveal Dcp2 has selectivity for the first transcribed nucleotide during the catalytic step. The heterotetrameric Edc1–Dcp1–Dcp2–Edc3 structure shows how coactivators Edc1 and Edc3 can act simultaneously to activate decapping catalysis.
Removal of the 5′ cap on mRNA by the decapping enzyme Dcp2 is a critical step in 5′-to-3′ mRNA decay. Understanding the structural basis of Dcp2 activity has been a significant challenge because Dcp2 is dynamic, with weak affinity for cap substrate. Here we present a 2.6-Å-resolution crystal structure of a heterotrimer of fission yeast Dcp2, its essential activator Dcp1, and the human NMD cofactor PNRC2, in complex with a tight-binding cap analog. Cap binding is accompanied by a conformational change of Dcp2 to form a composite nucleotide binding site using conserved residues on the catalytic and regulatory domains. Kinetic analysis of PNRC2 reveals a conserved short linear motif enhances both substrate affinity and the catalytic step of decapping. These findings explain why Dcp2 requires a conformational change for efficient catalysis and reveals that coactivators can promote RNA binding and the catalytic step of decapping, possibly through different conformational states.
Cap analogs are chemically modified derivatives of the unique cap structure present at the 5´ end of all eukaryotic mRNAs and several non-coding RNAs. Until recently, cap analogs have served primarily as tools in the study of RNA metabolism. Continuing advances in our understanding of cap biological functions (including RNA stabilization, pre-mRNA splicing, initiation of mRNA translation, as well as cellular transport of mRNAs and snRNAs) and the consequences of the disruption of these processes - resulting in serious medical disorders - have opened new possibilities for pharmaceutical applications of these compounds. In this review, the medicinal potential of cap analogs in areas, such as cancer treatment (including eIF4E targeting and mRNA-based immunotherapy), spinal muscular atrophy treatment, antiviral therapy and the improvement of the localization of nucleus-targeting drugs, are highlighted. Advances achieved to date, challenges, plausible solutions and prospects for the future development of cap analog-based drug design are described.
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