title: Structure determination of the small ubiquitin-related modifier SUMO-1.
abstract: 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.
authors.affiliation: Abteilung Physikalische Biochemie, Max-Planck-Institut für molekulare Physiologie, Dortmund, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Bayer
authors.forename: A
authors.initials: A
authors.lastname: Arndt
authors.forename: S
authors.initials: S
authors.lastname: Metzger
authors.forename: R
authors.initials: R
authors.lastname: Mahajan
authors.forename: F
authors.initials: F
authors.lastname: Melchior
authors.forename: R
authors.initials: R
authors.lastname: Jaenicke
authors.forename: J
authors.initials: J
authors.lastname: Becker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry; D025842:SUMO-1 Protein; D017386:Sequence Homology, Amino Acid; D014452:Ubiquitins / Q000737:chemistry*
chemical_list: D011994:Recombinant Proteins; D025842:SUMO-1 Protein; D014452:Ubiquitins