Structure And Regulatory Mechanism Of Streptococcus Pneumoniae Transcription Factor FabT In The Biosynthesis Of Fatty Acids

Streptococcus pneumoniae is a major human respiratory pathogen that causes millions of deaths each year in the world.However,due to the abuse of antibiotics,more and more bacteria had developed one or multi-drug resistance systems.Understanding the moleculer machanism of drug resistance and developing new antibiotics are very important for therapy of the related human diseases.Fatty acids systhesis(FAS)pathway has long been considered as a good target of novel antibiotics.FAS pathway provides the substrates for the biosynthesis of bacterial biofilms,and it is crucial for bacterial phospholipid homeostasis.Bacteria had evolved a variety of transcription factors to regulate FAS for the survival and adaption to diverse environments.Streptococci use the MarR family transcription factor FabT to negatively regulate the expression of FAS genes.Deletion of fabT leads to the increase of saturated fatty acidchains and longer fatty acid chains.However,the fine mechanism of FAS regulated by FabT remains poorly understood.Here we solved the crystal structure of FabT in complex with 23-bp palindromic DNA sequence derived from the fabK promoter region,and found that the structure of the FabT-DNA complex is similar to that of MarR family members.Further analysis of the DNA-binding pattern showed that FabT binds to DNA in a relatively looser manner,compared with other complex structures of MarR homologs.We synthesized the long-chain acyl-ACP in vitro,and demonstrated that it could increase the binding affinity of FabT towards DNA.Combined with electrostatic potential analysis and sequence alignment,we docked long-chain acyl-ACP on FabT-DNA,and obtained a reliable binding model.This model showed that the acidic ACP interacts with a basic region of FabT,with the long-chain fatty acid inserting in a hydrophobic pocket of FabT.Furthermore,the docking model was proved by mutantions of the corresponding residues combined with binding assays.Altogether,these findings help us to better understand the regulatory mechanism of bacterial FAS and provide the structural basis for rational designof novel antibiotics that prevent the infection of S.pneumoniae.