Dan Su

Recent studies have shown that lysines can be posttranslationally modified by various types of acylations. However, except for acetylation, very little is known about their scope and cellular distribution. We mapped thousands of succinylation sites in bacteria (E. coli), yeast (S. cerevisiae), human (HeLa) cells, and mouse liver tissue, demonstrating widespread succinylation in diverse organisms. A majority of succinylation sites in bacteria, yeast, and mouse liver were acetylated at the same position. Quantitative analysis of succinylation in yeast showed that succinylation was globally altered by growth conditions and mutations that affected succinyl-coenzyme A (succinyl-CoA) metabolism in the tricarboxylic acid cycle, indicating that succinylation levels are globally affected by succinyl-CoA concentration. We preferentially detected succinylation on abundant proteins, suggesting that succinylation occurs at a low level and that many succinylation sites remain unidentified. These data provide a systems-wide view of succinylation and its dynamic regulation and show its extensive overlap with acetylation.

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 SUMO2/3 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. Using a peptide-level immunoprecipitation enrichment strategy, we identify 14,869 endogenous SUMO2/3 sites in human cells during heat stress and proteasomal inhibition, and quantitatively map 1963 SUMO sites across eight mouse tissues. Characterization of the SUMO equilibrium highlights striking differences in SUMO metabolism between cultured cancer cells and normal tissues. Targeting preferences of SUMO2/3 vary 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.

Abstract Tectons are defined as molecules whose interactions are dominated by specific attractive forces that induce the assembly of aggregates with controlled geometries; molecular tectonics is the art and science of supramolecular construction using tectonic subunits. Intermolecular hydrogen bonds offer a particularly effective force for promoting controlled tectonic aggregation, and tectons able to participate in extensive networks of hydrogen bonds can be constructed by the simple expedient of attaching multiple 2-pyridone subunits to carefully chosen molecular frameworks. For example, tectons that incorporate four tetrahedrally oriented 2-pyridone subunits are predisposed to generate diamondoid networks or related three-dimensional lattices. As expected, crystallization of nominally tetrahedral tectons 8, 10, and 11 produces diamondoid hydrogen-bonded networks with distances between the centers of adjoining tectons varying from approximately 12 to 20 Å. These networks define large internal volumes that are filled by a combination of independent interpenetrating diamond networks and enclathrated guests. Such networks are porous enough to permit the exchange of guests and robust enough to remain intact, even though their structural integrity is maintained only by hydrogen bonding. Three-dimensional hydrogen-bonded networks not based on diamond can be generated by the association of related tectons, including stannane 13, that incorporate features designed to make them more deformable. These observations are important because they suggest that clever application of the strategy of molecular tectonics can be used to build an unlimited range of ordered three-dimensional organic networks with some of the desirable properties of zeolites and related inorganic materials, including high structural integrity, potentially large void volumes, and adjustable microporosity.