Phosphorylation of RanGAP1 stabilizes its interaction with Ran and RanBP1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Ran GTPase is crucial for nuclear transport, spindle formation, and nuclear envelope reassembly.
• RanGAP1, a Ran-specific GTPase activating protein, is a key regulator of Ran.
• The regulatory mechanisms controlling RanGAP1 activity in nucleocytoplasmic transport remain under investigation.

Purpose of the Study:

• To investigate the post-translational modifications of RanGAP1.
• To identify the specific phosphorylation site(s) on RanGAP1 and the responsible kinase.
• To determine the functional consequences of RanGAP1 phosphorylation on the Ran system.

Main Methods:

• In vivo and in vitro phosphorylation assays.
• Mass spectrometry (MALDI-TOF-MS) for site identification.
• Site-directed mutagenesis to confirm phosphorylation site.
• Recombinant kinase experiments and inhibitor studies.
• Analysis of ternary complex formation (Ran, RanBP1, RanGAP1).

Main Results:

• RanGAP1 is phosphorylated in vivo and in vitro, with Serine-358 identified as the major site.
• Casein kinase II (CK2) was identified as the kinase responsible for phosphorylating RanGAP1 at Serine-358.
• Phosphorylation at Serine-358 did not significantly alter the GTPase activating protein (GAP) activity of RanGAP1.
• Phosphorylated wild-type RanGAP1, but not a Serine-358 mutant, efficiently formed a stable ternary complex with Ran and RanBP1 in vivo.

Conclusions:

• RanGAP1 undergoes phosphorylation at Serine-358, primarily mediated by CK2.
• Serine-358 phosphorylation of RanGAP1 influences its interaction within the Ran system, affecting complex formation with Ran and RanBP1.
• These findings suggest a regulatory mechanism for nucleocytoplasmic transport through the modulation of RanGAP1 activity via phosphorylation.