Insights into the Microscopic Structure of RNF4-SIM-SUMO Complexes from MD Simulations

Area of Science:

• Biochemistry
• Structural Biology
• Computational Biology

Background:

• Post-translational modification by small ubiquitin-like modifiers (SUMO) impacts thousands of human proteins.
• SUMOylation events are translated into functional outcomes through the binding of SUMO to SUMO interacting motifs (SIMs).
• The E3 ubiquitin ligase RNF4, featuring multiple SIMs, links SUMOylation to the ubiquitin pathway, with SIM2 and SIM3 being key for recognizing SUMO chains.

Purpose of the Study:

• To investigate the properties of complexes formed by SUMO3 with peptides containing SIM2 or SIM3 using molecular dynamics simulations.
• To determine the affinities of these SIM-SUMO complexes using a free energy protocol and compare with experimental data.
• To provide a new interpretation of the SIM-SUMO interface structure and identify key interaction sites.

Main Methods:

• Molecular dynamics (MD) simulations were employed to study SUMO3-peptide complexes.
• A state-of-the-art free energy protocol was utilized to determine binding affinities.
• Long unrestrained simulations were performed to analyze the structural dynamics of the SIM-SUMO interface.

Main Results:

• The calculated affinities of SUMO3-SIM2 and SUMO3-SIM3 complexes agreed well with experimental data.
• Both SIM2 and SIM3 were observed to bind SUMO3 in parallel and antiparallel orientations.
• Key interaction sites involving acidic residues flanking the SIMs were identified, and unusual interfaces in a previously reported NMR structure were noted.

Conclusions:

• The computational method accurately characterizes individual SIM-SUMO complexes.
• The study provides insights into the binding modes and affinities of SUMO3 with SIM2 and SIM3 peptides.
• Further research is needed to understand these interactions in multivalent contexts.