||The SUMO protein was named Small Ubiquitin-like MOdifier because its 3-D structure was similar to Ubiquitin. In human, three SUMO proteins were discovered, namely, SUMO-1/2/3. The recombinant △1-8, 94-95 SUMO-2 protein with 10 histidine residues at its N-terminus was expressed using E. coli. BL-21(DE3), purified at 4 oC and crystallized at room temperature. The surface properties of human SUMO-1/2/3 proteins and 3-D structure of △1-8, 94-95 SUMO-2 protein were analyzed using computer modeling and X-ray diffraction technology respectively.|
The two-step purification by immobilized metal ion affinity chromatography(IMAC) was developed to yield △1-8, 94-95 SUMO-2 protein that reached 60 mg/ml for crystallization. On protein expression, 120 mg protein was obtained from 6 L bacterial growth broth. Crystals of △1-8, 94-95 SUMO-2 were obtained by the hanging-drop vapor diffusion method and many different crystal forms were observed. One of single crystal with triangular plate polyhedron form diffracted to 1.6 Å resolution, the other one with rectangular polyhedron form diffracted to 1.2 Å. Analysis of the diffraction pattern suggests the crystals belong to R3 space group, the former one owned unit cell parameters a= b=75.3 Å, c=29.2 Å, α=90°, β=90°,γ=120°, and the later one owned unit cell parameters a= b=74.9 Å, c=33.2 Å and the same angles respectively.
The R factor and Rfree of refinement are 0.133 and 0.190 with highly precise phase on 3-D structure of SUMO-2 protein. Comparison of crystal structure between human SUMO-2 and yeast SMT3 showed that the r.m.s. deviation of Cα coordinate is 1.054 Å. In addition, comparison of SUMO-1 NMR structure and SMT3 crystal structure showed that the r.m.s. deviation of Cα coordinates is 2.736 Å. Hence, the structures of SUMO-2 and SMT3 are more similar each other than those of SUMO-1and SMT3.