Biological cleavage of lignin bonds BRC Science Highlight Biological cleavage of lignin bonds Objective Test the proficiency of three sphingomonad bacteria to break the β-aryl ether bond of a model lignin dimer and characterize enzymes in the β-etherase lignin degradation pathway for their activities. Approach Test dimeric aromatic compound metabolism rates of sphingomonads using guaiacylglycerol-β-guiacyl ether (GGE) as the substrate. Determine activity of the Nu-class glutathione S-transferase (GST) from Novosphingobium aromaticivorans. Perform crystallographic and modeling studies for NaGSTNu to propose reaction mechanism. Evaluate Nu-class GSTs from other bacterial species. Results/Impacts N. aromaticivorans was found to metabolize GGE at one of the fastest rates thus far reported, making it an attractive organism for studying various aspects of the β-etherase lignin degradation pathway. The Nu-class glutathione S-transferase NaGSTNu is the only enzyme required to remove glutathione from the resulting phenylpropanoid conjugate stereoisomers after the ether bond is broken in this pathway. Crystallographic structural studies and molecular modeling yielded a proposed mechanism for the NaGSTNu glutathione lyase reaction. Understanding this bacterial pathway for breaking lignin bonds can aid future efforts to develop microbial systems for converting ligno-cellulosic biomass into commodities. Notes: text Title again: Text 1-2 sentence summary? Structure of NaGSTNu (PDB 5UUO). A) domain structure of one subunit of the homodimer (with the open C-terminal configuration). B) contacts between active-site residues and the GSH1 and GSH2 dithiol and the GS-SG disulphide. Kontur, W. S. et al. “Novosphingobium aromaticivorans uses a Nu-class glutathione S-transferase as a glutathione lyase in breaking the β-aryl ether bond of lignin.” Journal of Biological Chemistry 293, 4955-4968 (2018) [DOI: 10.1074/jbc.RA117.001268]. GLBRC April 2018