Modification of Ran GTPase-activating protein by the small ubiquitin-related modifier SUMO-1 requires Ubc9, an E2-type ubiquitin-conjugating enzyme homologue.
Covalent modification of the Ran GTPase-activating protein RanGAP1 with the ubiquitin-related protein SUMO-1 promotes its association with Nup358, a component of the cytoplasmic fibrils emanating from the nuclear pore complex (1,2). In Xenopus egg extracts, Nup358 can be found in a complex with Ubc9 (3), a structural homologue of the E2-type ubiquitin-conjugating enzymes (UBCs). Here we show that a subset of the human homologue of Ubc9 (HsUbc9) colocalizes with RanGAP1 at the nuclear envelope. HsUbc9 forms thiolester conjugates with recombinant SUMO-1, but not with recombinant ubiquitin, indicating that it is functionally distinct from E2-type UBCs. Finally, HsUbc9 is required for the modification of RanGAP1 by SUMO-1. These results suggest that HsUbc9 is a component of a novel enzymatic cascade that modifies RanGAP1, and possibly other substrates, with SUMO-1.
Lee
G W
GW
Brigham and Women's Hospital, Division of Rheumatology, Boston, Massachusetts 02115, USA. glee@rics.bwh.harvard.edu
Melchior
F
F
Matunis
M J
MJ
Mahajan
R
R
Tian
Q
Q
Anderson
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006801:Humans; D008025:Ligases / Q000145:classification / Q000378:metabolism*; D009154:Mutation; D009685:Nuclear Envelope / Q000201:enzymology*; D011233:Precipitin Tests; D011485:Protein Binding; D051381:Rats; D025842:SUMO-1 Protein; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes; D014452:Ubiquitins / Q000378:metabolism*; D029867:Xenopus Proteins; D000098843:Ubiquitin-Conjugating Enzyme UBC9
D002352:Carrier Proteins; D020690:GTPase-Activating Proteins; C092317:RANGAP1 protein, human; C513268:RanGAP1 protein, Xenopus; D025842:SUMO-1 Protein; D013438:Sulfhydryl Compounds; D014452:Ubiquitins; D029867:Xenopus Proteins; D000255:Adenosine Triphosphate; D044763:Ubiquitin-Conjugating Enzymes; D008025:Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9