Structural basis for protein functional transfer by SUMOylation

已知人类热休克因子2 （hHSF2）在其DNA结合域和三聚域内被SUMOylated。SUMOylation对DNA结合活性的正面和负面影响均有报道。为了探讨SUMOylation对hHSF2 DNA结合活性的调控机制，我们分析了hHSF2 DNA结合域（DBD）的DNA结合活性，并观察了SUMOylation的作用。结果表明，SUMOylation降低了hHSF2 DBD的DNA结合活性。核磁共振和脉冲ESR实验以及模型构建的结果表明，SUMO片段在SUMO附着的hHSF2 DBD上并不固定，因此相对于hHSF2 DBD的位置不同，但SUMO片段倾向于靠近hSF2 DBD的推定DNA结合表面。我们提出附着SUMO随机抑制DNA进入。我们确定了SUMO-3配合物的核磁共振结构和MCAF1的sumo -相互作用基序（SIM）。该结构暗示存在两个界面，分别介导疏水和静电相互作用。后者可能与MCAF1 SIM优先结合SUMO-2/3而非SUMO-1有关。我们已经确定了UHRF1与半甲基化DNA复合物中SRA结构域的晶体结构。在这个复合体中，一个甲基基被翻转出来，并插入到SRA的口袋中。该结构表明翻转机制对甲基基识别很重要。

Human Heat Shock Factor 2 (hHSF2) has been known to be SUMOylated within its DNA binding domain and trimerization domain. Both positive and negative effect on DNA binding activity by SUMOylation had been reported. In order to investigate the mechanism of regulation of DNAbinding activity of hHSF2 by SUMOylation, we analyzed DNA binding activity of the DNA binding domain (DBD) of hHSF2 and observed the effect of SUMOylation. The result indicated that SUMOylation decreases DNA binding activity of hHSF2 DBD. The results of NMR and pulse ESR experiments and model building suggest that the SUMO moiety on SUMO-attached hHSF2 DBD is not fixed, and thus diversely positioned relative to hHSF2 DBD, but the SUMO moiety tend to be in proximity to the putative DNA binding surface of hSF2 DBD. We proposed the attached SUMO stochastically inhibits DNA access.We have determined NMR structure of complex of SUMO-3 and the SUMO-interacting motif (SIM) of MCAF1. The structure implies the existence of two interfaces, which mediate mainly hydrophobic and electrostatic interactions, respectively. The latter might be involved in the preferential binding to SUMO-2/3 over SUMO-1 by MCAF1 SIM.We have determined the crystal structure of the SRA domain of UHRF1 in complex with hemi-methylated DNA. In the complex, a methyl base is flipped out, and is inserted into a pocket of SRA. The structure implies that the flip out mechanism is important for methyl base recognition.