SUMOylated RanGAP1 prepared by click chemistry

A stable chemical SUMO1-Ubc9 conjugate specifically binds as a thioester mimic to the RanBP2-E3 ligase complex

Ubiquitin and ubiquitin-like (Ubl) modifiers such as SUMO are conjugated to substrate proteins by E1, E2, and E3 enzymes. In the presence of an E3 ligase, the E2∼Ubl thioester intermediate becomes highly activated and is prone to chemical decomposition, thus making biochemical and structural studies difficult. Here we explored a stable chemical conjugate of the E2 enzyme from the SUMO pathway, Ubc9, with its modifier SUMO1 as a structural analogue of the Ubc9∼SUMO1 thioester intermediate, by introducing a triazole linkage by biorthogonal click chemistry. The chemical conjugate proved stable against proteolytic cleavage, in contrast to a Ubc9-SUMO1 isopeptide analogue obtained by auto-SUMOylation. Triazole-linked Ubc9-SUMO1 bound specifically to the preassembled E3 ligase complex RanBP2/RanGAP1*SUMO1/Ubc9, thus suggesting that it is a suitable thioester mimic. We anticipate interesting prospects for its use as a research tool to study protein complexes involving E2 and E3 enzymes.

One-pot chemical synthesis of small ubiquitin-like modifier protein-peptide conjugates using bis(2-sulfanylethyl)amido peptide latent thioester surrogates

Small ubiquitin-like modifier (SUMO) post-translational modification (PTM) of proteins has a crucial role in the regulation of important cellular processes. This protocol describes the chemical synthesis of functional SUMO-peptide conjugates. The two crucial stages of this protocol are the solid-phase synthesis of peptide segments derivatized by thioester or bis(2-sulfanylethyl)amido (SEA) latent thioester functionalities and the one-pot assembly of the SUMO-peptide conjugate by a sequential native chemical ligation (NCL)/SEA native peptide ligation reaction sequence. This protocol also enables the isolation of a SUMO SEA latent thioester, which can be attached to a target peptide or protein in a subsequent step. It is compatible with 9-fluorenylmethoxycarbonyl (Fmoc) chemistry, and it gives access to homogeneous, reversible and functional SUMO conjugates that are not easily produced using living systems. The synthesis of SUMO-peptide conjugates on a milligram scale takes 20 working days.

A novel PEG-based solid support enables the synthesis of >50 amino-acid peptide thioesters and the total synthesis of a functional SUMO-1 peptide conjugate

Bis(2-sulfanylethyl)amino PEG resin gives access to large peptide thioester segments and to functional SUMO-1 conjugates.