title: Mass spectrometry-based sequencing of lignin oligomers.
abstract: Although the primary structure of proteins, nucleic acids, and carbohydrates can be readily determined, no sequencing method has been described yet for the second most abundant biopolymer on earth (i.e. lignin). Within secondary-thickened plant cell walls, lignin forms an aromatic mesh arising from the combinatorial radical-radical coupling of monolignols and many other less abundant monomers. This polymerization process leads to a plethora of units and linkage types that affect the physicochemical characteristics of the cell wall. Current methods to analyze the lignin structure focus only on the frequency of the major monomeric units and interunit linkage types but do not provide information on the presence of less abundant unknown units and linkage types, nor on how linkages affect the formation of neighboring linkages. Such information can only be obtained using a sequencing approach. Here, we describe, to our knowledge for the first time, a sequencing strategy for lignin oligomers using mass spectrometry. This strategy was then evaluated on the oligomers extracted from wild-type poplar (Populus tremula x Populus tremuloides) xylem. In total, 134 lignin trimers to hexamers were observed, of which 36 could be completely sequenced. Interestingly, based on molecular mass data of the unknown monomeric and dimeric substructures, at least 10 unknown monomeric units or interunit linkage types were observed, one of which was identified as an arylglycerol end unit.
authors.affiliation: Department of Plant Systems Biology, Flanders Institute for Biotechnology, B-9052 Ghent, Belgium.
authors.forename: Kris
authors.initials: K
authors.lastname: Morreel
authors.forename: Oana
authors.initials: O
authors.lastname: Dima
authors.forename: Hoon
authors.initials: H
authors.lastname: Kim
authors.forename: Fachuang
authors.initials: F
authors.lastname: Lu
authors.forename: Claudiu
authors.initials: C
authors.lastname: Niculaes
authors.forename: Ruben
authors.initials: R
authors.lastname: Vanholme
authors.forename: Rebecca
authors.initials: R
authors.lastname: Dauwe
authors.forename: Geert
authors.initials: G
authors.lastname: Goeminne
authors.forename: Dirk
authors.initials: D
authors.lastname: Inzé
authors.forename: Eric
authors.initials: E
authors.lastname: Messens
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Wout
authors.initials: W
authors.lastname: Boerjan
mesh_terms: D002473:Cell Wall / Q000737:chemistry; D008031:Lignin / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods*; D015394:Molecular Structure; D032107:Populus / Q000737:chemistry*; D017421:Sequence Analysis / Q000379:methods*; D052584:Xylem / Q000737:chemistry
chemical_list: D008031:Lignin