Capping DNA with DNA.

Area of Science:

• Molecular Biology
• Biochemistry
• Synthetic Biology

Background:

• Deoxyribozymes are DNA molecules with catalytic activity.
• ATP (adenosine triphosphate) is the primary energy currency of cells.
• DNA ligation, often performed by protein enzymes like T4 DNA ligase, creates specific DNA structures.

Purpose of the Study:

• To isolate and characterize novel deoxyribozymes capable of ATP-dependent self-capping reactions.
• To investigate the catalytic mechanism and structural features of these deoxyribozymes.
• To explore the potential of DNA enzymes in performing functions typically requiring protein enzymes.

Main Methods:

• In vitro selection from a random-sequence DNA pool to isolate catalytic deoxyribozymes.
• Biochemical assays to measure catalytic efficiency using ATP or dATP as substrates.
• Chemical probing and site-directed mutagenesis to elucidate the active structure, including the role of guanine quartets.

Main Results:

• Twelve classes of deoxyribozymes were identified, catalyzing the transfer of the AMP moiety of ATP to their 5'-terminal phosphate, forming a 5',5'-pyrophosphate linkage.
• A specific 41-nucleotide deoxyribozyme (class 1) requires Cu(2+) and recognizes both adenine and triphosphate groups of ATP/dATP.
• The catalytic efficiency was measured at 10(4) M(-1) min(-1), comparable to other catalytic nucleic acids, with guanine quartets implicated in the active structure.

Conclusions:

• DNA enzymes can perform ATP-dependent self-charging reactions, creating a DNA adenylate structure similar to that formed by T4 DNA ligase.
• These deoxyribozymes demonstrate significant catalytic activity and possess specific structural requirements, including cofactor dependence and recognition of ATP moieties.
• The findings suggest that DNA alone can be engineered to carry out complex reactions essential for DNA cloning, potentially replacing protein enzymes.