ADP-ribosylation factor-directed GTPase-activating protein. Purification and partial characterization

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• ADP-ribosylation factor (ARF) proteins regulate vesicular traffic and phospholipase D activity.
• ARF activation depends on GTP binding, and GTP hydrolysis serves as an off signal.
• GTP hydrolysis by ARFs requires a GTPase-activating protein (GAP) due to low intrinsic GTPase activity.

Purpose of the Study:

• To purify and characterize the GTPase-activating protein (GAP) for ADP-ribosylation factor (ARF) from rat liver cytosol.
• To investigate the properties and structure of the purified ARF GAP.
• To understand the regulatory mechanisms of ARF proteins in cellular processes.

Main Methods:

• Purification of ARF GAP from rat liver cytosol using denaturing agents and assessing refolding capacity.
• Protein purification involved approximately 15,000-fold enrichment.
• Characterization included SDS-PAGE, Superdex 200 gel filtration, and partial amino acid sequencing.

Main Results:

• A 49 kDa ARF GAP was purified, identified as a previously uncharacterized protein.
• The purified GAP exhibited a tetrameric structure (200 kDa complex) in solution.
• The ARF GAP activity was stimulated by phosphoinositides and inhibited by phosphatidylcholine.

Conclusions:

• The complete purification of a novel ARF GAP from rat liver cytosol was achieved.
• The purified ARF GAP is a 49 kDa protein with a tetrameric structure, regulated by specific lipids.
• This purified ARF GAP molecule provides a valuable tool for studying ARF protein-mediated cellular functions.