Structural basis for protein functional transfer by SUMOylation

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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.