Structure determination of the small ubiquitin-related modifier SUMO-1

J Mol Biol. 1998 Jul 10;280(2):275-86. doi: 10.1006/jmbi.1998.1839.


The recently discovered small ubiquitin-related modifier SUMO-1 belongs to the growing family of ubiquitin-related proteins involved in postranslational protein modification. Unlike ubiquitin, SUMO-1 does not appear to target proteins for degradation but seems to be involved in the modulation of protein-protein interactions. Independent studies demonstrate an essential function of SUMO-1 in the regulation of nucleo-cytoplasmic transport, and suggest a role in cell-cycle regulation and apoptosis. Here, we present the first three-dimensional structure of SUMO-1 solved by NMR. Although having only 18% amino acid sequence identity with ubiquitin, the overall structure closely resembles that of ubiquitin, featuring the betabetaalphabetabetaalphabeta fold of the ubiquitin protein family. In addition, the position of the two C-terminal Gly residues required for isopeptide bond formation is conserved between ubiquitin and SUMO-1. The most prominent feature of SUMO-1 is a long and highly flexible N terminus, which protrudes from the core of the protein and which is absent in ubiquitin. Furthermore, ubiquitin Lys48, required to generate ubiquitin polymers, is substituted in SUMO-1 by Gln69 at the same position, which provides an explanation of why SUMO-1 has not been observed to form polymers. Moreover, the hydrophobic core of SUMO-1 and ubiquitin is maintained by conserved hydrophobic residues, whereas the overall charge topology of SUMO-1 and ubiquitin differs significantly, suggesting specific modifying enzymes and target proteins for both proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Humans
  • Magnetic Resonance Spectroscopy
  • Molecular Sequence Data
  • Protein Conformation
  • Protein Folding
  • Recombinant Proteins / chemistry
  • SUMO-1 Protein
  • Sequence Homology, Amino Acid
  • Ubiquitins / chemistry*


  • Recombinant Proteins
  • SUMO-1 Protein
  • Ubiquitins