The role of the SUMO pathway in regulation of the nuclear function.

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1)We developed a binary vector system that introduces a synthetic SUMO-1 conjugation pathway into Escherichia coli and demonstrated that large amounts of sumoylated Ran GTPase activating protein 1 C-terminal region(RanGAP1-C2), Ran binding protein 2 internal repeat domain, p53 and promyelocytic leukemia were efficiently produced. The sumoylated recombinant RanGAP1-C2 appeared to retain the in vivo properties, since it was specifically sumoylated at lysine 517 as expected from in vivo studies. Our findings indicate the establishment of a biosynthetic route for producing large amounts of sumoylated recombinant proteins that will open up new avenues for studying the biochemical and structural aspects of the SUMO-1 modification pathway.(see FEBS Lett.564,85-90,2004 and Anal.Biochem.331,204-206,2004)2)We show that RanBP2's 30-kDa catalytic fragment is a largely unstructured protein. Despite two distinct but partially overlapping 79-residue catalytic domains, one of which is sufficient for maximal activity, RanBP2 binds to Ubc9 in a 1:1 stoichiometry. The identification of nine RanBP2 and three Ubc9 side chains that are important for RanBP2-dependent SUMOylation indicates largely hydrophobic interactions. These properties distinguish RanBP2 from all other known E3 ligases, and we speculate that RanBP2 exerts its catalytic effect by altering Ubc9's properties rather than by mediating target interactions.(see Nat.Struct.Mol.Biol.11,984-989,2004)