Fructose-1,6-bisphosphatase from Synechococcus leopoliensis. Substrate-dependent dimer-tetramer interconversion

Area of Science:

• Biochemistry
• Enzymology
• Cyanobacterial Metabolism

Background:

• Synechococcus leopoliensis (Anacystis nidulans) possesses two D-fructose-1,6-bisphosphatase (FBPase) forms, A and B.
• Form B accounts for the majority of extractable FBPase activity and has been purified.

Purpose of the Study:

• To investigate the quaternary structure and activation mechanism of FBPase form B from S. leopoliensis.
• To compare the regulatory properties of FBPase forms A and B.

Main Methods:

• Purification of FBPase form B to homogeneity.
• Gel filtration and non-denaturing polyacrylamide gel electrophoresis to assess subunit composition.
• Cross-linking with bis(sulfosuccinimidyl)suberate to study oligomeric states.
• Investigation of substrate (fructose-1,6-bisphosphate and Mg2+) dependency.

Main Results:

• FBPase form B exists as a dimer or tetramer, with interconversion dependent on fructose-1,6-bisphosphate and Mg2+.
• The dimer-tetramer transition is reversible.
• A two-step activation mechanism for FBPase B is proposed: reduction of the dimer followed by substrate-dependent conversion to the active tetramer.
• FBPase form A did not exhibit substrate-dependent oligomeric interconversion.

Conclusions:

• FBPase form B from S. leopoliensis undergoes a reversible dimer-tetramer transition regulated by substrates.
• The catalytically active form of FBPase B is the reduced tetramer.
• FBPase form A appears to be regulated differently, lacking substrate-dependent oligomerization.