680 / 2019-04-30 23:00:43

New insight into lignin biosynthesis: P450 complex formation and electron shuttle

Lignin,p450,Protein complex,Electron shuttle

全体主题 > Cell Biology

Lignin is a complex and irregular biopolymer that support secondary cell wall for water conductance and plant strength. Its biosynthesis requires three endoplasmic reticulum (ER)-resident cytochrome P450 monooxygenases, C4H, C3ʹ H and F5H, which were postulated to associate with each other and/or potentially with other soluble monolignol biosynthetic enzymes to form an enzyme complex. However, the molecular basis governing such enzyme organization and functioning remains elusive. We conducted immunoprecipitation (IP) coupled with Liquid chromatography-mass spectrometry (LC-MS) to identify the potential protein complex associated with these P450 enzymes in Arabidopsis; by which, we discovered multiple potential P450 interacting proteins. Among them, we found that Arabidopsis membrane steroid-binding proteins (MSBPs) serve as a scaffold to physically organize monolignol P450 monooxygenases, thereby regulating the lignin biosynthetic process; while cytochrome b5 isoform D (CB5D) is an indispensable electron shuttle protein specific for S-lignin biosynthesis. Downregulation of MSBP genes substantially impaired the stability and activity of the MSBP-interacting P450 enzymes and, consequently, the total lignin content, while disrupting CB5D resulted in >60% reduction of S lignin subunits but showed no impairment on G-lignin formation, supporting key roles of MSBPs and CB5D in lignin biosynthesis.