Markov State Study of Electrostatic Channeling within the Tricarboxylic Acid Cycle Supercomplex

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Supramolecular enzyme nanoassemblies (metabolons) exhibit high catalytic efficiency.
• Enzyme proximity in metabolons facilitates direct intermediate transport between active sites.
• Electrostatic channeling is a key mechanism for efficient intermediate transfer.

Purpose of the Study:

• To investigate the molecular mechanism of intermediate transport in the malate dehydrogenase (MDH) and citrate synthase (CS) supercomplex.
• To identify the specific residues and pathways involved in oxaloacetate (OAA) transfer via electrostatic channeling.
• To validate computational findings with experimental mutagenesis data.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model the enzyme complex.
• Markov state models (MSMs) were constructed to analyze OAA transport pathways.
• A hub score approach was used to identify critical residues controlling transport.
• Site-directed mutagenesis (Arginine to Alanine) was performed to test computational predictions.

Main Results:

• MSM analysis identified dominant pathways for OAA transport from MDH to CS.
• A small set of residues, including a specific arginine, were identified as crucial for OAA transport.
• Mutating the identified arginine residue resulted in a 2-fold decrease in transfer efficiency, consistent with experimental data.

Conclusions:

• This study provides a detailed molecular-level understanding of electrostatic channeling in enzyme supercomplexes.
• The identified key residues are critical for efficient intermediate transport.
• The findings enable the rational design of novel catalytic nanostructures for enhanced chemical synthesis and biofuel applications.