Construction Of Metabolic Pathway For Lignin Degradation Using Metabolic Recombination Model

Lignin is the second abundant biological resource in nature,which is only inferior to cellulose.As a natural polymer,the biodegradation of lignin is always a difficult problem.Through physical,chemical and biological methods,the complex polymer structure of lignin can be destroyed to obtain a series of phenolic derivatives such as4-hydroxybenzoic acid,protocatechuic acid and catechol.Phenolic substances are difficult to be used by most microorganisms,which makes it difficult for the microbial degradation of lignin.In order to better design the pathway of biodegradation of lignin,a biochemical metabolic network was constructed by integrating all biochemical reactions,compounds and enzymes in the KEGG database.A procedure was designed to calculate the connecting paths between any two compounds in the biological metabolic network in a short time,and a metabolic reorganization model was constructed to calculate the rearrangement and combination process of all metabolic pathways.Using all the biological metabolic reactions completed by the current analysis,a computational biological metabolic network was constructed.Input the number of two compounds into the program,and the program can calculate all possible connection paths of these two compounds in the whole network and output the calculation results one by one.Efficient design of relatively complete transformation path extends the method and strategy of genetic engineering design of metabolic path to a new dimension of systematization and modeling.In order to better enable microorganisms to degrade lignin and synthesize some target products,multiple pathways of various lignin monomers and their derivatives to convert to acetyl coenzyme A were calculated through the metabolic recombination model.According to different types of initial substrates,all the path maps were drawn into the degradation path maps of H-type,G-type and S-type lignin monomers and their derivatives.The figure shows the relatively complete theoretical path of lignin degradation to acetyl coenzyme A.The results showed that 4-hydroxybenzoic acid was the core intermediate compound in the degradation process of H-type lignin monomer and derivatives,and the degradation transited to the downstream long carbon chain degradation link under the action of different ring opening enzymes.The core intermediate compound for the degradation of G-type lignin monomer and derivative is3,4-dihydroxybenzoic acid,while the degradation of S-type lignin monomer and derivative is the most complex,which usually requires the removal of a methoxy group and incorporation of 3,4-dihydroxybenzoic acid to open the ring.Based on the calculated results of recombination paths,the thermodynamic feasibility and theoretical yields of different degradation paths were discussed through yield models.As the practical application of metabolic recombination model,these calculation results expand the lignin biodegradation strategy,and can design biodegradation paths for many difficult to degrade substances,so that microorganisms can use these difficult to degrade substances and synthesize desired target products.