The phosphate carrier from yeast mitochondria. Dimerization is a prerequisite for function

Area of Science:

• Biochemistry
• Molecular Biology
• Mitochondrial Transport

Background:

• The mitochondrial phosphate carrier (PIC) from Saccharomyces cerevisiae is essential for cellular energy metabolism.
• Understanding the oligomeric state and functional mechanism of PIC is key to elucidating mitochondrial transport processes.

Purpose of the Study:

• To investigate the functional oligomeric state of the yeast phosphate carrier (PIC).
• To determine if PIC functions as a monomer or dimer and characterize the stability and activity of these forms.

Main Methods:

• Expression and isolation of wild-type and recombinant PIC proteins from E. coli.
• Detergent exchange and dialysis to achieve stable PIC dimers.
• Affinity chromatography using differentially tagged monomers to create defined homo- and heterodimers.
• Reconstitution of PIC monomers and dimers into liposomes to assess transport activity.

Main Results:

• PIC was isolated as partially monomeric and unfolded, forming stable dimers upon detergent exchange and dialysis.
• Reconstitution of PIC dimers showed a linear dependence of transport activity on protein amount, unlike the sigmoidal dependence for monomers.
• Heterodimers with one active and one inactive subunit were inactive, while mixtures of active and inactive monomers showed partial activity.
• PIC dimers are stable in solution and after membrane insertion.

Conclusions:

• Phosphate carrier (PIC) does not function in its monomeric form.
• PIC functions as a stable dimer in both solubilized and membrane-inserted states.
• Phosphate transport mediated by PIC dimers involves functional cross-talk between the two monomers.