title: Systems biology of lignin biosynthesis in Populus trichocarpa: heteromeric 4-coumaric acid:coenzyme A ligase protein complex formation, regulation, and numerical modeling.
abstract: As a step toward predictive modeling of flux through the pathway of monolignol biosynthesis in stem differentiating xylem of Populus trichocarpa, we discovered that the two 4-coumaric acid:CoA ligase (4CL) isoforms, 4CL3 and 4CL5, interact in vivo and in vitro to form a heterotetrameric protein complex. This conclusion is based on laser microdissection, coimmunoprecipitation, chemical cross-linking, bimolecular fluorescence complementation, and mass spectrometry. The tetramer is composed of three subunits of 4CL3 and one of 4CL5. 4CL5 appears to have a regulatory role. This protein-protein interaction affects the direction and rate of metabolic flux for monolignol biosynthesis in P. trichocarpa. A mathematical model was developed for the behavior of 4CL3 and 4CL5 individually and in mixtures that form the enzyme complex. The model incorporates effects of mixtures of multiple hydroxycinnamic acid substrates, competitive inhibition, uncompetitive inhibition, and self-inhibition, along with characteristic of the substrates, the enzyme isoforms, and the tetrameric complex. Kinetic analysis of different ratios of the enzyme isoforms shows both inhibition and activation components, which are explained by the mathematical model and provide insight into the regulation of metabolic flux for monolignol biosynthesis by protein complex formation.
authors.affiliation: State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, Harbin 150040, China.
authors.forename: Hsi-Chuan
authors.initials: HC
authors.lastname: Chen
authors.forename: Jina
authors.initials: J
authors.lastname: Song
authors.forename: Jack P
authors.initials: JP
authors.lastname: Wang
authors.forename: Ying-Chung
authors.initials: YC
authors.lastname: Lin
authors.forename: Joel
authors.initials: J
authors.lastname: Ducoste
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Shuford
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Quanzi
authors.initials: Q
authors.lastname: Li
authors.forename: Rui
authors.initials: R
authors.lastname: Shi
authors.forename: Angelito
authors.initials: A
authors.lastname: Nepomuceno
authors.forename: Fikret
authors.initials: F
authors.lastname: Isik
authors.forename: David C
authors.initials: DC
authors.lastname: Muddiman
authors.forename: Cranos
authors.initials: C
authors.lastname: Williams
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Sederoff
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Chiang
mesh_terms: D003066:Coenzyme A Ligases / Q000235:genetics / Q000378:metabolism*; D003373:Coumaric Acids / Q000378:metabolism*; D047468:Immunoprecipitation; D008031:Lignin / Q000096:biosynthesis*; D013058:Mass Spectrometry; D008954:Models, Biological; D032107:Populus / Q000378:metabolism*; D011422:Propionates; D012333:RNA, Messenger / Q000235:genetics; D013379:Substrate Specificity; D049490:Systems Biology
chemical_list: D003373:Coumaric Acids; D011422:Propionates; D012333:RNA, Messenger; D008031:Lignin; D003066:Coenzyme A Ligases; C495469:p-coumaric acid