Crystal structures of the human SUMO-2 protein at 1.6 A and 1.2 A resolution: implication on the functional differences of SUMO proteins.
The SUMO proteins are a class of small ubiquitin-like modifiers. SUMO is attached to a specific lysine side chain on the target protein via an isopeptide bond with its C-terminal glycine. There are at least four SUMO proteins in humans, which are involved in protein trafficking and targeting. A truncated human SUMO-2 protein that contains residues 9-93 was expressed in Escherichia coli and crystallized in two different unit cells, with dimensions of a=b=75.25 A, c=29.17 A and a=b=74.96 A, c=33.23 A, both belonging to the rhombohedral space group R3. They diffracted X-rays to 1.6 A and 1.2 A resolution, respectively. The structures were determined by molecular replacement using the yeast SMT3 protein as a search model. Subsequent refinements yielded R/Rfree values of 0.169/0.190 and 0.119/0.185, at 1.6 A and 1.2 A, respectively. The peptide folding of SUMO-2 consists of a half-open beta-barrel and two flanking alpha-helices with secondary structural elements arranged as betabetaalphabetabetaalphabeta in the sequence, identical to those of ubiquitin, SMT3 and SUMO-1. Comparison of SUMO-2 with SUMO-1 showed a surface region near the C terminus with significantly different charge distributions. This may explain their distinct intracellular locations. In addition, crystal-packing analysis suggests a possible trimeric assembly of the SUMO-2 protein, of which the biological significance remains to be determined.
Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan.
Wen-Chen
WC
Huang
Tzu-Ping
TP
Ko
Steven S-L
SS
Li
Andrew H-J
AH
Wang
D000595:Amino Acid Sequence; D003460:Crystallization / Q000379:methods; D018360:Crystallography, X-Ray / Q000379:methods; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D025841:Small Ubiquitin-Related Modifier Proteins / Q000737:chemistry* / Q000502:physiology; D055672:Static Electricity; D025801:Ubiquitin / Q000737:chemistry / Q000235:genetics
D011994:Recombinant Proteins; C117909:SUMO2 protein, human; D025841:Small Ubiquitin-Related Modifier Proteins; D025801:Ubiquitin