Preparation and characterization of lignin-protein covalent linkages.

摘要

Lignin is a natural aromatic polymer that is bio-synthesized in the cell walls of almost all land plants. Great strides have been made in understanding lignin's biological origins and chemical and physical properties. However, many unanswered questions remain. For example, the extent to which lignin interacts with other cell wall components, such as proteins, is largely unknown. In order to help address this question, the preparation and characterization of lignin-protein covalent linkages is reported here for the first time. Chapter 1 provides a more detailed introduction, justification, and literature review.;Chapter 2 focuses on the preparation of low molecular weight lignin-protein model compounds. The compounds were not prepared under biomimetic conditions. Instead, the primary focus of this study was on the characterization of the model compounds, leading to the identification of diagnostic lignin-protein NMR chemical shifts.;Chapter 3 describes the characterization of lignin-protein linkages prepared under biomimetic conditions of lignin DHP formation. NMR showed that cysteine and tyrosine containing peptides covalently crosslink with lignin, while other amino acids do not. IR and EDS were useful for showing the general incorporation of protein into the lignin, but were incapable of distinguishing covalent and non-covalent interactions.;Chapter 4 describes the interaction between lignin and gelatin protein. It was found, using EDS and IR, that gelatin was incorporated into lignin DHP. However, a lack of diagnostic NMR signatures revealed that the crosslinking was likely dominated by non-covalent interactions such as physical entanglement. This seems likely, as gelatin is lacking in both cysteine and tyrosine residues, which were shown to be the only reactive amino acids towards lignin.;Chapter 5 details attempts at identifying lignin-protein linkages in wild type Arabidopsis. Arabidopsis was grown to maturity, then lignin was extracted from cell wall material using acidified dioxane. Elemental analysis was used to show that the lignin was contaminated with about 3.75% protein; however, NMR was not able to identify lignin-protein covalent linkages.;Chapter 6 details some future experiments that could be used to explore lignin-protein linkages, and it is hoped that this work will pave the way for such studies.