Endogenous, in vivo, and site-specific characterization of the SUMO architecture across species and organs

Small ubiquitin-like modifiers (SUMOs) are post-translational modifications that play crucial roles in most cellular processes. While methods exist to study exogenous SUMOylation, large-scale characterization of endogenous SUMO has remained technically daunting. Here, we describe a proteomics approach facilitating system-wide and in vivo identification of lysines modified by endogenous and native SUMO2/3. We identified 14,869 endogenous SUMO sites in human cells during heat stress and proteasomal inhibition, and mapped 1,963 SUMO sites across eight mouse tissues; brain, heart, kidney, lung, liver, muscle, spleen, and testis. Quantification of the SUMO equilibrium highlighted striking differences in SUMO metabolism, between cells and tissues. Targeting preferences of SUMO varied across different organ types, coinciding with markedly differential SUMOylation states of all enzymes involved in the SUMO conjugation cascade. Collectively, our systemic investigation details the SUMOylation architecture across species and organs and provides a resource of endogenous SUMOylation sites on factors important in organ-specific functions and disease.