Fhit-nucleotide specificity probed with novel fluorescent and fluorogenic substrates.

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• The histidine triad superfamily protein, Fhit, acts as a tumor suppressor in human epithelial cancers.
• Fhit's tumor suppressor function is linked to its ability to form substrate complexes, independent of its diadenosine polyphosphate cleavage activity.

Purpose of the Study:

• To quantify interactions between Fhit and competitive inhibitors.
• To investigate Fhit's substrate binding and inhibition using novel fluorophore-containing diadenosine polyphosphate analogs.

Main Methods:

• Synthesis of fluorophore-conjugated diadenosine polyphosphate analogs (ApppAMC, ApppBODIPY, GpppBODIPY).
• Utilizing fluorescence assays to measure Fhit substrate cleavage and competitive inhibition.
• Determining kinetic parameters (K(m), K(I)) for various inhibitors including diadenosine polyphosphates, pyrophosphate, and mononucleotides.

Main Results:

• Novel fluorophore analogs were synthesized and demonstrated to be effective Fhit substrates.
• GpppBODIPY cleavage resulted in a significant fluorescence increase due to BODIPY quenching by guanine.
• Pyrophosphate was found to be a more effective competitor than purine mononucleotides, indicating Fhit's discrimination against cellular competitors.

Conclusions:

• Fhit discriminates substrates based on catalytic efficiency (k(cat)) and cellular competitors based on binding affinity.
• The study provides insights into Fhit's molecular interactions relevant to its tumor suppressor role.
• Pyrophosphate's strong competitive binding highlights its potential significance in Fhit regulation.