Shedding light on the interaction between TMPyP4 and human telomeric quadruplexes.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The binding of TMPyP4 to G-quadruplex structures, particularly from human telomeric DNA, lacks a definitive model.
• Human telomeric G-quadruplexes exhibit complex polymorphism in solution, which is simplified under molecular crowding.

Purpose of the Study:

• To systematically investigate the binding of TMPyP4 to human telomeric G-quadruplexes under dilute and molecular crowding conditions.
• To elucidate the binding stoichiometry, conformational effects, and selectivity of TMPyP4 for G-quadruplex DNA.

Main Methods:

• Isothermal titration calorimetry (ITC) to quantify binding thermodynamics and stoichiometry.
• Circular dichroism (CD) spectroscopy to monitor conformational changes upon TMPyP4 binding.

Main Results:

• All studied G-quadruplexes bind up to four TMPyP4 molecules.
• In dilute solution, TMPyP4 induces a conformational shift from hybrid to antiparallel G-quadruplex structures.
• Under molecular crowding, TMPyP4 binding does not induce significant conformational changes.
• Binding occurs in two sequential steps: initial interaction of one TMPyP4 molecule, followed by binding of three more.
• TMPyP4 demonstrates enhanced selectivity for G-quadruplex DNA over duplex DNA under molecular crowding.

Conclusions:

• TMPyP4 exhibits a consistent binding stoichiometry of 1:4 (quadruplex:TMPyP4) across different conditions.
• Solution conditions significantly influence TMPyP4-induced G-quadruplex conformational dynamics.
• Enhanced G-quadruplex selectivity under molecular crowding supports TMPyP4's potential therapeutic applications.