Testing the sulfotransferase molecular pore hypothesis.

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Human cytosolic sulfotransferases (SULTs) are crucial enzymes involved in the metabolism of numerous signaling molecules.
• SULTs catalyze the transfer of a sulfuryl group from 3"-phosphoadenosine 5 -phosphosulfate (PAPS) to various substrates.
• Understanding SULT substrate selectivity is vital for drug development and understanding metabolic pathways.

Purpose of the Study:

• To investigate the role of a molecular pore and nucleotide binding in controlling SULT substrate selectivity.
• To test the proposed pore model of SULT selectivity using site-directed mutagenesis in SULT2A1.
• To elucidate the structural and functional basis of SULT substrate discrimination.

Main Methods:

• Utilized site-directed mutagenesis to disrupt specific molecular linkages in SULT2A1.
• Assessed the impact of mutations on enzyme selectivity and catalytic efficiency towards different substrate sizes.
• Employed molecular dynamics modeling to predict and analyze pore dynamics and substrate access.

Main Results:

• Mutations in SULT2A1 successfully uncoupled nucleotide binding from substrate selectivity.
• Mutant enzymes lost discrimination between large and small substrates, showing a 183-fold increase in catalytic efficiency for large substrates.
• A structural analysis confirmed that an 11-residue flap can open to allow large substrate entry upon nucleotide binding.

Conclusions:

• The study validates a pore-based model for SULT substrate selectivity, highlighting the dynamic nature of the enzyme's active site.
• Nucleotide-dependent conformational changes, particularly pore isomerization and flap movement, are critical for SULT selectivity.
• These findings provide a framework for understanding and potentially engineering SULT activity and selectivity for therapeutic applications.