Structure of a 10-23 deoxyribozyme exhibiting a homodimer conformation

Catalytic mechanisms of the 8-17 and 10-23 DNAzymes: shared mechanistic strategies

RNA-cleaving DNAzymes have emerged as promising catalytic nucleic acids with potential applications in biotechnology and therapeutics. Among them, the 10-23 and 8-17 DNAzymes, both derived from the same in vitro selection experiment, have emerged as the most widely studied RNA-cleaving DNAzymes due to their high catalytic efficiency and broad metal ion dependence. Despite their apparent structural differences, recent structural, functional, and computational studies have revealed convergent catalytic strategies in their mechanisms. This review examines the commonalities between the 8-17 and 10-23 DNAzymes, offering a comparative mechanistic perspective on the catalytic strategies underlying their RNA cleavage activity, following the nomenclature proposed by Breaker et al. We discuss recent evidence from functional, crystallographic, NMR-based, and molecular dynamics studies that highlight how conserved guanine residues act as general bases, while hydrated metal ions contribute as general acids in both DNAzymes. By summarizing the latest advancements in the field, this review aims to provide a comprehensive perspective on the fundamental catalytic strategies employed by the 8-17 and the 10-23 DNAzymes and their relevance for future applications in nucleic acid-based catalysis.

Prebiotic RNA self-assembling and the origin of life: Mechanistic and molecular modeling rationale for explaining the prebiotic origin and replication of RNA

In recent years, a great interest has been focused on the prebiotic origin of nucleic acids and life on Earth. An attractive idea is that life was initially based on an autocatalytic and autoreplicative RNA (the RNA-world). RNA duplexes are right-handed helical chains with antiparallel orientation, but the rationale for these features is not yet known. An antiparallel (inverted) stacking of purine nucleosides was reported in crystallographic studies. Molecular modeling also supports the inverted orientation of nucleosides. This preferential stacking can also appear when nucleosides are included in a montmorillonite clay matrix. Free-energy values and geometrical parameters show that D-ribose chirality is preferred for the formation of right-handed RNA molecules. Thus, a "zipper" model with antiparallel and auto-intercalated nucleosides linked by phosphate groups can be proposed to form single RNA chains. Unstacking with strand separation and base pairing by H-bonding, results in shortening and inclination of ribose-phosphate chains, leading to right-handed helicity and antiparallel duplexes. Incorporation of complementary precursors on the major groove template by a self-assembly mechanism provides a prebiotic (non-enzymatic) "tetris" replication model by formation of a transient RNA tetrad and tetraplex. Original hairpin motifs appear as simple building units that form typical RNA structures such as hammerheads, cloverleaves and dumbbells. They occur today in the circular viroids and virusoids, as well as in highly branched and complex rRNA molecules.

A review towards sustainable analyte detection: Biomimetic inspiration in biosensor technology

The branch of biomimetics has witnessed a profound impact on the field of biosensor technology, reflected in sustainable analyte detection. A vast array of biosensor platforms with improved/upgraded performance have been developed and reported. No wonder the motivation from the field of biomimetics has a huge impact on generating detection systems with escalated degrees of manipulation and tunability at different levels. More recently, biomimetic biosensor technology has found potential in constructing bio-inspired materials such as aptamers, MIPs, nanozymes, DNAzymes, Synzymes, etc. to be integrated with biosensor fabrication. The establishment of a sensing setup is not limited to the bioreceptor fabrication; the construction of transducing element using biomimetic material have been reported too. Moreover, to serve a biosensing of target analyte from a fatal diseased sample different biomimetic architectures can be designed that mimic in-vivo microenvironmental surroundings to get an exact microenvironment equivalent to natural conditions leading towards designing of a precise treatment strategy. This research area is ever-evolving as there is a scope for upgradation and refinement due to advancing technologies including nanotechnology, biomimetic nanomaterials, microfluidics, optical sensors, etc. This review is an attempt to comprehend and juxtapose the very primary innovations in the field of biomimetic biosensor technology to realize its comprehensive and wide-range scope and possibilities.

Advancing cancer treatments: The role of oligonucleotide-based therapies in driving progress

Although recent advancements in cancer immunology have resulted in the approval of numerous immunotherapies, minimal progress has been observed in addressing hard-to-treat cancers. In this context, therapeutic oligonucleotides, including interfering RNAs, antisense oligonucleotides, aptamers, and DNAzymes, have gained a central role in cancer therapeutic approaches due to their capacity to regulate gene expression and protein function with reduced toxicity compared with conventional chemotherapeutics. Nevertheless, systemic administration of naked oligonucleotides faces many extra- and intracellular challenges that can be overcome by using effective delivery systems. Thus, viral and non-viral carriers can improve oligonucleotide stability and intracellular uptake, enhance tumor accumulation, and increase the probability of endosomal escape while minimizing other adverse effects. Therefore, gaining more insight into fundamental mechanisms of actions of various oligonucleotides and the challenges posed by naked oligonucleotide administration, this article provides a comprehensive review of the recent progress on oligonucleotide delivery systems and an overview of completed and ongoing cancer clinical trials that can shape future oncological treatments.

Exploring the catalytic mechanism of the 10-23 DNAzyme: insights from pH-rate profiles

The 10-23 DNAzyme, a catalytic DNA molecule with RNA-cleaving activity, has garnered significant interest for its potential therapeutic applications as a gene-silencing agent. However, the lack of a detailed understanding about its mechanism has hampered progress. A recent structural analysis has revealed a highly organized conformation thanks to the stabilization of specific interactions within the catalytic core of the 10-23 DNAzyme, which facilitate the cleavage of RNA. In this configuration, it has been shown that G14 is in good proximity to the cleavage site which suggests its role as a general base, by activating the 2'-OH nucleophile, in the catalysis of the 10-23 DNAzyme. Also, the possibility of a hydrated metal acting as a general acid has been proposed. In this study, through activity assays, we offer evidence of the involvement of general acid-base catalysis in the mechanism of the 10-23 DNAzyme by analyzing its pH-rate profiles and the role of G14, and metal cofactors like Mg2+ and Pb2+. By substituting G14 with its analogue 2-aminopurine and examining the resultant pH-rate profiles, we propose the participation of G14 in a catalytically relevant proton transfer event, acting as a general base. Further analysis, using Pb2+ as a cofactor, suggests the capability of the hydrated metal ion to act as a general acid. These functional results provide critical insights into the catalytic strategies of RNA-cleaving DNAzymes, revealing common mechanisms among nucleic acid enzymes that cleave RNA.

The Effect of 8,5'-Cyclo 2'-deoxyadenosine on the Activity of 10-23 DNAzyme: Experimental and Theoretical Study

The in vivo effectiveness of DNAzymes 10-23 (Dz10-23) is limited due to the low concentration of divalent cations. Modifications of the catalytic loop are being sought to increase the activity of Dz10-23 in physiological conditions. We investigated the effect of 5'S or 5'R 5',8-cyclo-2'deoxyadenosine (cdA) on the activity of Dz10-23. The activity of Dz10-23 was measured in a cleavage assay using radiolabeled RNA. The Density Functional Tight Binding methodology with the self-consistent redistribution of Mulliken charge modification was used to explain different activities of DNAzymes. The substitution of 2'-deoxyadenosine with cdA in the catalytic loop decreased the activity of DNAzymes. Inhibition was dependent on the position of cdA and its absolute configuration. The order of activity of DNAzymes was as follows: wt-Dz > ScdA5-Dz ≈ RcdA15-Dz ≈ ScdA15-Dz > RcdA5-Dz. Theoretical studies revealed that the distance between phosphate groups at position 5 in RcdA5-Dz was significantly increased compared to wt-Dz, while the distance between O4 of dT4 and nonbonding oxygen of PO2 attached to 3'O of dG2 was much shorter. The strong inhibitory effect of RcdA5 may result from hampering the flexibility of the catalytic loop (increased rigidity), which is required for the proper positioning of Me2+ and optimal activity.