Helicase-like functions in phosphate loop containing beta-alpha polypeptides.

Area of Science:

• Biochemistry
• Molecular Evolution
• Structural Biology

Background:

• The P-loop Walker A motif is crucial for hundreds of essential enzyme families, including nucleotide triphosphates (NTPs) binding and phosphoryl transfer (P-loop NTPases).
• The evolutionary origins of these complex enzymes from simpler precursors remain an open question.
• Prior research demonstrated that P-loops in simple βα repeat proteins bind NTPs, ssDNA, and RNA.

Purpose of the Study:

• To investigate the evolutionary origins of P-loop NTPases.
• To explore whether simple polypeptides could exhibit enzymatic activities beyond ligand binding.
• To demonstrate rudimentary helicase-like functions in minimal P-loop structures.

Main Methods:

• Construction of simple 40-residue polypeptides containing a single β-(P-loop)-α element.
• Assays to evaluate DNA strand separation, exchange, and unwinding activities.
• Binding kinetics and low-resolution structural analyses of polypeptide assemblies.

Main Results:

• Minimal P-loop polypeptides demonstrated strand separation and exchange functions.
• These polypeptides were capable of unwinding double-stranded DNA (dsDNA).
• Activity was mediated by oligomeric forms (dimers to high-order assemblies), suggesting a role for dynamic assembly.

Conclusions:

• Simple P-loop prototypes exhibit plausible sequence, structure, and function of early P-loop NTPases.
• Multifunctionality and dynamic assembly in short polypeptides were key to developing complex, evolutionarily relevant functions.
• These findings provide a model for the emergence of primordial P-loop enzymes from simple peptide precursors.