Regulation and quaternary structural changes in rabbit muscle phosphofructokinase

Area of Science:

• Biochemistry
• Enzymology
• Protein Structure and Dynamics

Background:

• Phosphofructokinase (PFK) is a key regulatory enzyme in glycolysis.
• Subunit assembly, conformational changes, and post-translational modifications influence PFK activity.
• High-resolution structural data for rabbit muscle PFK in active/inactive states is lacking.

Purpose of the Study:

• To investigate the structure-function correlation of rabbit muscle PFK using phosphorylation as a probe.
• To elucidate the role of subunit assembly in PFK activity regulation.
• To understand structural changes associated with PFK activation.

Main Methods:

• Sedimentation velocity to monitor PFK subunit self-association.
• Circular dichroism (CD) spectroscopy to assess secondary structure.
• Fluorescence quenching to probe tryptophan accessibility to solvent.
• Steady-state kinetics to correlate physical properties with enzyme activity.

Main Results:

• Phosphorylation did not alter PFK's self-assembly mechanism or secondary structure.
• Tryptophan accessibility to solvent decreased with increasing protein concentration (oligomer formation).
• PFK activation by substrate involved quaternary structural changes, not secondary/tertiary modifications, with reduced tryptophan accessibility.

Conclusions:

• Post-translational modification and subunit association do not significantly alter PFK subunit structure but affect tryptophan residue accessibility.
• PFK activation involves quaternary structural rearrangement of subunit-subunit interactions.
• Subunit assembly is intrinsically linked to the regulation of rabbit muscle PFK activity.