Crystal Structures Of Two TetR Family Transcriptional Factors And Their Complexes With DNA

Transcriptional regulation is very important for microbial adaptation to multiple environmental conditions.However,the involved structural mechanismes which these transcriptional factors regulate expression of diverse genes remain largely unclear.In this study,we focused on the crystal structures of two TetR family transcription factors,LtmA and InbR,in mycobacteria,and main results include:Firstly,series of truncated mutants for two regulators were designed and the stable mutant proteins in solubility and digestion-resistance were successfully characterized.Several crystals,including native LtmA and InbR and their corresponding methionine selenium proteins,were obtained through the vapor phase diffusion method.Next,the three-dimensional structures of these protein crystals were solved successfully by using multiple wavelength anomalous scattering method.The overall structure of LtmA and InbR are similar to that of other typical TFRs which are composed of the N-terminal DNA-binding domain(DBD)and the C-terminal ligand binding domain(LBD).The homo-tetramer of LtmA is composed of two longer a8 and a9 helixes and a shorter a4 helix.InbR is composed of 10 alpha helixes.The shorter a6 and α10 control LBD s two exports respectively and broad its ligand selectivity,While the longer a4 increases the obstruction of conformational change.Finally,the optimal length of DNA fragments bound by LtmA and InbR were identified by Electrophoretic Mobility Shift Assay(EMSA)and gel chromatography,and their complex crystals in 2 A and 2.5 A resolution have been obtained.In conclusion,we have successfully solved crystal structures of two TetR family of transcriptional factors,LtmA and InbR.These provide a basis for further understanding of the interaction mechanisms between the TetR family transcription factors and DNA.