Broad spectrum identification of cellular small ubiquitin-related modifier (SUMO) substrate proteins.

Reversible covalent modification of proteins with a small ubiquitin-related modifier (SUMO) is emerging as an important system contributing to dynamic regulation of protein function. To enhance our understanding of the cell regulatory systems impacted by sumoylation, we used affinity chromatography-coupled high pressure liquid chromatography/tandem mass spectrometry for unbiased identification of candidate cellular SUMO substrate proteins. Here we describe the identification of 21 candidate sumoylated proteins from whole-cell lysates of HEK-293 cells. The nature of the proteins identified is consistent with a role for sumoylation in diverse cell regulatory systems but highlights regulation of chromatin organization and gene expression as major systems targeted by the sumoylation machinery.