Ran-GTPase activating protein 1 (RanGAP1, Swiss:P46061) is a GTPase activator for the nuclear Ras-related regulatory protein Ran, converting it to the putatively inactive GDP-bound state. Its C-terminal domain is required for RanGAP1 localisation at the vertebrate nuclear pore complex, and is sumoylated by the small ubiquitin-related modifier protein (SUMO-1, Swiss:Q93068). This domain is composed almost entirely of helical substructures that are organised into an alpha-alpha superhelix fold, with the exception of the peptide containing the lysine residue required for SUMO-1 conjugation [1].

1: Structural basis for E2-mediated SUMO conjugation revealed by a complex between ubiquitin-conjugating enzyme Ubc9 and RanGAP1. Bernier-Villamor V, Sampson DA, Matunis MJ, Lima CD; Cell 2002;108:345-356. PMID:11853669