Biochemical Characterization of a Human Septin Octamer

Area of Science:

• Cell Biology
• Cytoskeleton Dynamics
• Protein Biochemistry

Background:

• Septins are P-loop GTPases forming heteromeric filaments crucial for cellular processes.
• The precise roles of GTP binding and hydrolysis in septin polymerization and dynamics remain unclear.

Purpose of the Study:

• To investigate the polymerization mechanism of human septin rods.
• To elucidate the role of the SEPT9 subunit in filament formation.
• To characterize the nucleotide binding and hydrolysis properties of human septins.

Main Methods:

• Purification of recombinant human septin octamers from E. coli.
• In vitro polymerization assays.
• Kinetic analysis of nucleotide uptake, exchange, and hydrolysis.

Main Results:

• Human septin rods polymerize into filaments in vitro.
• The C-terminal region of SEPT9 is critical for filament formation.
• Septin rods inhibit in vitro actin polymerization.
• Nucleotide uptake and exchange are dynamic, but hydrolyzed phosphate release is impaired.

Conclusions:

• Human septin filament formation is regulated by specific subunits and can influence actin dynamics.
• GTP hydrolysis in human septins likely follows a non-canonical pathway, distinct from other small GTPases.